diff --git a/src/Api/Controller/ListDiscussionsController.php b/src/Api/Controller/ListDiscussionsController.php
index dc825d9cd..c2b4af6d9 100644
--- a/src/Api/Controller/ListDiscussionsController.php
+++ b/src/Api/Controller/ListDiscussionsController.php
@@ -11,10 +11,10 @@ namespace Flarum\Api\Controller;
 
 use Flarum\Api\Serializer\DiscussionSerializer;
 use Flarum\Discussion\Discussion;
+use Flarum\Discussion\Filter\DiscussionFilterer;
 use Flarum\Discussion\Search\DiscussionSearcher;
 use Flarum\Http\UrlGenerator;
 use Flarum\Search\SearchCriteria;
-use Illuminate\Support\Arr;
 use Psr\Http\Message\ServerRequestInterface;
 use Tobscure\JsonApi\Document;
 
@@ -43,11 +43,21 @@ class ListDiscussionsController extends AbstractListController
         'lastPost'
     ];
 
+    /**
+     * {@inheritDoc}
+     */
+    public $sort = ['lastPostedAt' => 'desc'];
+
     /**
      * {@inheritdoc}
      */
     public $sortFields = ['lastPostedAt', 'commentCount', 'createdAt'];
 
+    /**
+     * @var DiscussionFilterer
+     */
+    protected $filterer;
+
     /**
      * @var DiscussionSearcher
      */
@@ -59,11 +69,13 @@ class ListDiscussionsController extends AbstractListController
     protected $url;
 
     /**
+     * @param DiscussionFilterer $filterer
      * @param DiscussionSearcher $searcher
      * @param UrlGenerator $url
      */
-    public function __construct(DiscussionSearcher $searcher, UrlGenerator $url)
+    public function __construct(DiscussionFilterer $filterer, DiscussionSearcher $searcher, UrlGenerator $url)
     {
+        $this->filterer = $filterer;
         $this->searcher = $searcher;
         $this->url = $url;
     }
@@ -74,16 +86,19 @@ class ListDiscussionsController extends AbstractListController
     protected function data(ServerRequestInterface $request, Document $document)
     {
         $actor = $request->getAttribute('actor');
-        $query = Arr::get($this->extractFilter($request), 'q');
+        $filters = $this->extractFilter($request);
         $sort = $this->extractSort($request);
 
-        $criteria = new SearchCriteria($actor, $query, $sort);
-
         $limit = $this->extractLimit($request);
         $offset = $this->extractOffset($request);
-        $load = array_merge($this->extractInclude($request), ['state']);
+        $include = array_merge($this->extractInclude($request), ['state']);
 
-        $results = $this->searcher->search($criteria, $limit, $offset);
+        $criteria = new SearchCriteria($actor, $filters, $sort);
+        if (array_key_exists('q', $filters)) {
+            $results = $this->searcher->search($criteria, $limit, $offset);
+        } else {
+            $results = $this->filterer->filter($criteria, $limit, $offset);
+        }
 
         $document->addPaginationLinks(
             $this->url->to('api')->route('discussions.index'),
@@ -95,9 +110,9 @@ class ListDiscussionsController extends AbstractListController
 
         Discussion::setStateUser($actor);
 
-        $results = $results->getResults()->load($load);
+        $results = $results->getResults()->load($include);
 
-        if ($relations = array_intersect($load, ['firstPost', 'lastPost'])) {
+        if ($relations = array_intersect($include, ['firstPost', 'lastPost'])) {
             foreach ($results as $discussion) {
                 foreach ($relations as $relation) {
                     if ($discussion->$relation) {
diff --git a/src/Api/Controller/ListUsersController.php b/src/Api/Controller/ListUsersController.php
index 5f44c0984..6e7bb4f84 100644
--- a/src/Api/Controller/ListUsersController.php
+++ b/src/Api/Controller/ListUsersController.php
@@ -12,8 +12,8 @@ namespace Flarum\Api\Controller;
 use Flarum\Api\Serializer\UserSerializer;
 use Flarum\Http\UrlGenerator;
 use Flarum\Search\SearchCriteria;
+use Flarum\User\Filter\UserFilterer;
 use Flarum\User\Search\UserSearcher;
-use Illuminate\Support\Arr;
 use Psr\Http\Message\ServerRequestInterface;
 use Tobscure\JsonApi\Document;
 
@@ -40,6 +40,11 @@ class ListUsersController extends AbstractListController
         'joinedAt'
     ];
 
+    /**
+     * @var UserFilterer
+     */
+    protected $filterer;
+
     /**
      * @var UserSearcher
      */
@@ -51,11 +56,13 @@ class ListUsersController extends AbstractListController
     protected $url;
 
     /**
+     * @param UserFilterer $filterer
      * @param UserSearcher $searcher
      * @param UrlGenerator $url
      */
-    public function __construct(UserSearcher $searcher, UrlGenerator $url)
+    public function __construct(UserFilterer $filterer, UserSearcher $searcher, UrlGenerator $url)
     {
+        $this->filterer = $filterer;
         $this->searcher = $searcher;
         $this->url = $url;
     }
@@ -69,16 +76,19 @@ class ListUsersController extends AbstractListController
 
         $actor->assertCan('viewUserList');
 
-        $query = Arr::get($this->extractFilter($request), 'q');
+        $filters = $this->extractFilter($request);
         $sort = $this->extractSort($request);
 
-        $criteria = new SearchCriteria($actor, $query, $sort);
-
         $limit = $this->extractLimit($request);
         $offset = $this->extractOffset($request);
-        $load = $this->extractInclude($request);
+        $include = $this->extractInclude($request);
 
-        $results = $this->searcher->search($criteria, $limit, $offset, $load);
+        $criteria = new SearchCriteria($actor, $filters, $sort);
+        if (array_key_exists('q', $filters)) {
+            $results = $this->searcher->search($criteria, $limit, $offset);
+        } else {
+            $results = $this->filterer->filter($criteria, $limit, $offset);
+        }
 
         $document->addPaginationLinks(
             $this->url->to('api')->route('users.index'),
@@ -88,6 +98,6 @@ class ListUsersController extends AbstractListController
             $results->areMoreResults() ? null : 0
         );
 
-        return $results->getResults();
+        return $results->getResults()->load($include);
     }
 }
diff --git a/src/Discussion/Event/Searching.php b/src/Discussion/Event/Searching.php
index 138a4f469..dde2b47b9 100644
--- a/src/Discussion/Event/Searching.php
+++ b/src/Discussion/Event/Searching.php
@@ -9,8 +9,8 @@
 
 namespace Flarum\Discussion\Event;
 
-use Flarum\Discussion\Search\DiscussionSearch;
 use Flarum\Search\SearchCriteria;
+use Flarum\Search\SearchState;
 
 /**
  * @deprecated beta 16, remove beta 17
@@ -18,7 +18,7 @@ use Flarum\Search\SearchCriteria;
 class Searching
 {
     /**
-     * @var DiscussionSearch
+     * @var SearchState
      */
     public $search;
 
@@ -28,10 +28,10 @@ class Searching
     public $criteria;
 
     /**
-     * @param DiscussionSearch $search
+     * @param SearchState $search
      * @param \Flarum\Search\SearchCriteria $criteria
      */
-    public function __construct(DiscussionSearch $search, SearchCriteria $criteria)
+    public function __construct(SearchState $search, SearchCriteria $criteria)
     {
         $this->search = $search;
         $this->criteria = $criteria;
diff --git a/src/Discussion/Filter/AuthorFilterGambit.php b/src/Discussion/Filter/AuthorFilterGambit.php
new file mode 100644
index 000000000..616b8be38
--- /dev/null
+++ b/src/Discussion/Filter/AuthorFilterGambit.php
@@ -0,0 +1,72 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Discussion\Filter;
+
+use Flarum\Filter\FilterInterface;
+use Flarum\Filter\FilterState;
+use Flarum\Search\AbstractRegexGambit;
+use Flarum\Search\SearchState;
+use Flarum\User\UserRepository;
+use Illuminate\Database\Query\Builder;
+
+class AuthorFilterGambit extends AbstractRegexGambit implements FilterInterface
+{
+    /**
+     * @var \Flarum\User\UserRepository
+     */
+    protected $users;
+
+    /**
+     * @param \Flarum\User\UserRepository $users
+     */
+    public function __construct(UserRepository $users)
+    {
+        $this->users = $users;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getGambitPattern()
+    {
+        return 'author:(.+)';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function conditions(SearchState $search, array $matches, $negate)
+    {
+        $this->constrain($search->getQuery(), $matches[1], $negate);
+    }
+
+    public function getFilterKey(): string
+    {
+        return 'author';
+    }
+
+    public function filter(FilterState $filterState, string $filterValue, bool $negate)
+    {
+        $this->constrain($filterState->getQuery(), $filterValue, $negate);
+    }
+
+    protected function constrain(Builder $query, $rawUsernames, $negate)
+    {
+        $usernames = trim($rawUsernames, '"');
+        $usernames = explode(',', $usernames);
+
+        $ids = [];
+        foreach ($usernames as $username) {
+            $ids[] = $this->users->getIdForUsername($username);
+        }
+
+        $query->whereIn('discussions.user_id', $ids, 'and', $negate);
+    }
+}
diff --git a/src/Discussion/Filter/CreatedFilterGambit.php b/src/Discussion/Filter/CreatedFilterGambit.php
new file mode 100644
index 000000000..638d84884
--- /dev/null
+++ b/src/Discussion/Filter/CreatedFilterGambit.php
@@ -0,0 +1,61 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Discussion\Filter;
+
+use Flarum\Filter\FilterInterface;
+use Flarum\Filter\FilterState;
+use Flarum\Search\AbstractRegexGambit;
+use Flarum\Search\SearchState;
+use Illuminate\Database\Query\Builder;
+use Illuminate\Support\Arr;
+
+class CreatedFilterGambit extends AbstractRegexGambit implements FilterInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function getGambitPattern()
+    {
+        return 'created:(\d{4}\-\d\d\-\d\d)(\.\.(\d{4}\-\d\d\-\d\d))?';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function conditions(SearchState $search, array $matches, $negate)
+    {
+        $this->constrain($search->getQuery(), Arr::get($matches, 1), Arr::get($matches, 3), $negate);
+    }
+
+    public function getFilterKey(): string
+    {
+        return 'created';
+    }
+
+    public function filter(FilterState $filterState, string $filterValue, bool $negate)
+    {
+        preg_match('/^'.$this->getGambitPattern().'$/i', 'created:'.$filterValue, $matches);
+
+        $this->constrain($filterState->getQuery(), Arr::get($matches, 1), Arr::get($matches, 3), $negate);
+    }
+
+    public function constrain(Builder $query, ?string $firstDate, ?string $secondDate, $negate)
+    {
+        // If we've just been provided with a single YYYY-MM-DD date, then find
+        // discussions that were started on that exact date. But if we've been
+        // provided with a YYYY-MM-DD..YYYY-MM-DD range, then find discussions
+        // that were started during that period.
+        if (empty($secondDate)) {
+            $query->whereDate('created_at', $negate ? '!=' : '=', $firstDate);
+        } else {
+            $query->whereBetween('created_at', [$firstDate, $secondDate], 'and', $negate);
+        }
+    }
+}
diff --git a/src/Discussion/Filter/DiscussionFilterer.php b/src/Discussion/Filter/DiscussionFilterer.php
new file mode 100644
index 000000000..8ada10502
--- /dev/null
+++ b/src/Discussion/Filter/DiscussionFilterer.php
@@ -0,0 +1,40 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Discussion\Filter;
+
+use Flarum\Discussion\DiscussionRepository;
+use Flarum\Filter\AbstractFilterer;
+use Flarum\User\User;
+use Illuminate\Database\Eloquent\Builder;
+
+class DiscussionFilterer extends AbstractFilterer
+{
+    /**
+     * @var DiscussionRepository
+     */
+    protected $discussions;
+
+    /**
+     * @param DiscussionRepository $discussions
+     * @param array $filters
+     * @param array $filterMutators
+     */
+    public function __construct(DiscussionRepository $discussions, array $filters, array $filterMutators)
+    {
+        parent::__construct($filters, $filterMutators);
+
+        $this->discussions = $discussions;
+    }
+
+    protected function getQuery(User $actor): Builder
+    {
+        return $this->discussions->query()->select('discussions.*')->whereVisibleTo($actor);
+    }
+}
diff --git a/src/Discussion/Filter/HiddenFilterGambit.php b/src/Discussion/Filter/HiddenFilterGambit.php
new file mode 100644
index 000000000..133167a36
--- /dev/null
+++ b/src/Discussion/Filter/HiddenFilterGambit.php
@@ -0,0 +1,56 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Discussion\Filter;
+
+use Flarum\Filter\FilterInterface;
+use Flarum\Filter\FilterState;
+use Flarum\Search\AbstractRegexGambit;
+use Flarum\Search\SearchState;
+use Illuminate\Database\Query\Builder;
+
+class HiddenFilterGambit extends AbstractRegexGambit implements FilterInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function getGambitPattern()
+    {
+        return 'is:hidden';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function conditions(SearchState $search, array $matches, $negate)
+    {
+        $this->constrain($search->getQuery(), $negate);
+    }
+
+    public function getFilterKey(): string
+    {
+        return 'hidden';
+    }
+
+    public function filter(FilterState $filterState, string $filterValue, bool $negate)
+    {
+        $this->constrain($filterState->getQuery(), $negate);
+    }
+
+    protected function constrain(Builder $query, bool $negate)
+    {
+        $query->where(function ($query) use ($negate) {
+            if ($negate) {
+                $query->whereNull('hidden_at')->where('comment_count', '>', 0);
+            } else {
+                $query->whereNotNull('hidden_at')->orWhere('comment_count', 0);
+            }
+        });
+    }
+}
diff --git a/src/Discussion/Search/Gambit/UnreadGambit.php b/src/Discussion/Filter/UnreadFilterGambit.php
similarity index 53%
rename from src/Discussion/Search/Gambit/UnreadGambit.php
rename to src/Discussion/Filter/UnreadFilterGambit.php
index 33aac7c91..06e6efb8e 100644
--- a/src/Discussion/Search/Gambit/UnreadGambit.php
+++ b/src/Discussion/Filter/UnreadFilterGambit.php
@@ -7,21 +7,18 @@
  * LICENSE file that was distributed with this source code.
  */
 
-namespace Flarum\Discussion\Search\Gambit;
+namespace Flarum\Discussion\Filter;
 
 use Flarum\Discussion\DiscussionRepository;
-use Flarum\Discussion\Search\DiscussionSearch;
+use Flarum\Filter\FilterInterface;
+use Flarum\Filter\FilterState;
 use Flarum\Search\AbstractRegexGambit;
-use Flarum\Search\AbstractSearch;
-use LogicException;
+use Flarum\Search\SearchState;
+use Flarum\User\User;
+use Illuminate\Database\Query\Builder;
 
-class UnreadGambit extends AbstractRegexGambit
+class UnreadFilterGambit extends AbstractRegexGambit implements FilterInterface
 {
-    /**
-     * {@inheritdoc}
-     */
-    protected $pattern = 'is:unread';
-
     /**
      * @var \Flarum\Discussion\DiscussionRepository
      */
@@ -38,18 +35,35 @@ class UnreadGambit extends AbstractRegexGambit
     /**
      * {@inheritdoc}
      */
-    protected function conditions(AbstractSearch $search, array $matches, $negate)
+    public function getGambitPattern()
     {
-        if (! $search instanceof DiscussionSearch) {
-            throw new LogicException('This gambit can only be applied on a DiscussionSearch');
-        }
+        return 'is:unread';
+    }
 
-        $actor = $search->getActor();
+    /**
+     * {@inheritdoc}
+     */
+    protected function conditions(SearchState $search, array $matches, $negate)
+    {
+        $this->constrain($search->getQuery(), $search->getActor(), $negate);
+    }
 
+    public function getFilterKey(): string
+    {
+        return 'unread';
+    }
+
+    public function filter(FilterState $filterState, string $filterValue, bool $negate)
+    {
+        $this->constrain($filterState->getQuery(), $filterState->getActor(), $negate);
+    }
+
+    protected function constrain(Builder $query, User $actor, bool $negate)
+    {
         if ($actor->exists) {
             $readIds = $this->discussions->getReadIds($actor);
 
-            $search->getQuery()->where(function ($query) use ($readIds, $negate, $actor) {
+            $query->where(function ($query) use ($readIds, $negate, $actor) {
                 if (! $negate) {
                     $query->whereNotIn('id', $readIds)->where('last_posted_at', '>', $actor->marked_all_as_read_at ?: 0);
                 } else {
diff --git a/src/Discussion/Search/DiscussionSearch.php b/src/Discussion/Search/DiscussionSearch.php
deleted file mode 100644
index 4a07492b2..000000000
--- a/src/Discussion/Search/DiscussionSearch.php
+++ /dev/null
@@ -1,51 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\Discussion\Search;
-
-use Flarum\Search\AbstractSearch;
-
-/**
- * An object which represents the internal state of a search for discussions:
- * the search query, the user performing the search, the fallback sort order,
- * relevant post information, and a log of which gambits have been used.
- */
-class DiscussionSearch extends AbstractSearch
-{
-    /**
-     * {@inheritdoc}
-     */
-    protected $defaultSort = ['lastPostedAt' => 'desc'];
-
-    /**
-     * @var array
-     */
-    protected $relevantPostIds = [];
-
-    /**
-     * Get the related IDs for each result.
-     *
-     * @return int[]
-     */
-    public function getRelevantPostIds()
-    {
-        return $this->relevantPostIds;
-    }
-
-    /**
-     * Set the relevant post IDs for the results.
-     *
-     * @param array $relevantPostIds
-     * @return void
-     */
-    public function setRelevantPostIds(array $relevantPostIds)
-    {
-        $this->relevantPostIds = $relevantPostIds;
-    }
-}
diff --git a/src/Discussion/Search/DiscussionSearcher.php b/src/Discussion/Search/DiscussionSearcher.php
index edc755b8c..05a16a3bb 100644
--- a/src/Discussion/Search/DiscussionSearcher.php
+++ b/src/Discussion/Search/DiscussionSearcher.php
@@ -11,10 +11,10 @@ namespace Flarum\Discussion\Search;
 
 use Flarum\Discussion\DiscussionRepository;
 use Flarum\Discussion\Event\Searching;
-use Flarum\Search\AbstractSearch;
 use Flarum\Search\AbstractSearcher;
 use Flarum\Search\GambitManager;
 use Flarum\Search\SearchCriteria;
+use Flarum\Search\SearchState;
 use Flarum\User\User;
 use Illuminate\Contracts\Events\Dispatcher;
 use Illuminate\Database\Eloquent\Builder;
@@ -50,15 +50,10 @@ class DiscussionSearcher extends AbstractSearcher
         return $this->discussions->query()->select('discussions.*')->whereVisibleTo($actor);
     }
 
-    protected function getSearch(Builder $query, User $actor): AbstractSearch
-    {
-        return new DiscussionSearch($query->getQuery(), $actor);
-    }
-
     /**
      * @deprecated along with the Searching event, remove in Beta 17.
      */
-    protected function mutateSearch(AbstractSearch $search, SearchCriteria $criteria)
+    protected function mutateSearch(SearchState $search, SearchCriteria $criteria)
     {
         parent::mutateSearch($search, $criteria);
 
diff --git a/src/Discussion/Search/Gambit/AuthorGambit.php b/src/Discussion/Search/Gambit/AuthorGambit.php
deleted file mode 100644
index 819a8885b..000000000
--- a/src/Discussion/Search/Gambit/AuthorGambit.php
+++ /dev/null
@@ -1,57 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\Discussion\Search\Gambit;
-
-use Flarum\Discussion\Search\DiscussionSearch;
-use Flarum\Search\AbstractRegexGambit;
-use Flarum\Search\AbstractSearch;
-use Flarum\User\UserRepository;
-use LogicException;
-
-class AuthorGambit extends AbstractRegexGambit
-{
-    /**
-     * {@inheritdoc}
-     */
-    protected $pattern = 'author:(.+)';
-
-    /**
-     * @var \Flarum\User\UserRepository
-     */
-    protected $users;
-
-    /**
-     * @param \Flarum\User\UserRepository $users
-     */
-    public function __construct(UserRepository $users)
-    {
-        $this->users = $users;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    protected function conditions(AbstractSearch $search, array $matches, $negate)
-    {
-        if (! $search instanceof DiscussionSearch) {
-            throw new LogicException('This gambit can only be applied on a DiscussionSearch');
-        }
-
-        $usernames = trim($matches[1], '"');
-        $usernames = explode(',', $usernames);
-
-        $ids = [];
-        foreach ($usernames as $username) {
-            $ids[] = $this->users->getIdForUsername($username);
-        }
-
-        $search->getQuery()->whereIn('discussions.user_id', $ids, 'and', $negate);
-    }
-}
diff --git a/src/Discussion/Search/Gambit/CreatedGambit.php b/src/Discussion/Search/Gambit/CreatedGambit.php
deleted file mode 100644
index 3d24d5f0f..000000000
--- a/src/Discussion/Search/Gambit/CreatedGambit.php
+++ /dev/null
@@ -1,43 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\Discussion\Search\Gambit;
-
-use Flarum\Discussion\Search\DiscussionSearch;
-use Flarum\Search\AbstractRegexGambit;
-use Flarum\Search\AbstractSearch;
-use LogicException;
-
-class CreatedGambit extends AbstractRegexGambit
-{
-    /**
-     * {@inheritdoc}
-     */
-    protected $pattern = 'created:(\d{4}\-\d\d\-\d\d)(\.\.(\d{4}\-\d\d\-\d\d))?';
-
-    /**
-     * {@inheritdoc}
-     */
-    protected function conditions(AbstractSearch $search, array $matches, $negate)
-    {
-        if (! $search instanceof DiscussionSearch) {
-            throw new LogicException('This gambit can only be applied on a DiscussionSearch');
-        }
-
-        // If we've just been provided with a single YYYY-MM-DD date, then find
-        // discussions that were started on that exact date. But if we've been
-        // provided with a YYYY-MM-DD..YYYY-MM-DD range, then find discussions
-        // that were started during that period.
-        if (empty($matches[3])) {
-            $search->getQuery()->whereDate('created_at', $negate ? '!=' : '=', $matches[1]);
-        } else {
-            $search->getQuery()->whereBetween('created_at', [$matches[1], $matches[3]], 'and', $negate);
-        }
-    }
-}
diff --git a/src/Discussion/Search/Gambit/FulltextGambit.php b/src/Discussion/Search/Gambit/FulltextGambit.php
index ea3fe3ede..f57e13c76 100644
--- a/src/Discussion/Search/Gambit/FulltextGambit.php
+++ b/src/Discussion/Search/Gambit/FulltextGambit.php
@@ -9,24 +9,18 @@
 
 namespace Flarum\Discussion\Search\Gambit;
 
-use Flarum\Discussion\Search\DiscussionSearch;
 use Flarum\Post\Post;
-use Flarum\Search\AbstractSearch;
 use Flarum\Search\GambitInterface;
+use Flarum\Search\SearchState;
 use Illuminate\Database\Query\Expression;
-use LogicException;
 
 class FulltextGambit implements GambitInterface
 {
     /**
      * {@inheritdoc}
      */
-    public function apply(AbstractSearch $search, $bit)
+    public function apply(SearchState $search, $bit)
     {
-        if (! $search instanceof DiscussionSearch) {
-            throw new LogicException('This gambit can only be applied on a DiscussionSearch');
-        }
-
         // Replace all non-word characters with spaces.
         // We do this to prevent MySQL fulltext search boolean mode from taking
         // effect: https://dev.mysql.com/doc/refman/5.7/en/fulltext-boolean.html
diff --git a/src/Discussion/Search/Gambit/HiddenGambit.php b/src/Discussion/Search/Gambit/HiddenGambit.php
deleted file mode 100644
index e658ba0e6..000000000
--- a/src/Discussion/Search/Gambit/HiddenGambit.php
+++ /dev/null
@@ -1,41 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\Discussion\Search\Gambit;
-
-use Flarum\Discussion\Search\DiscussionSearch;
-use Flarum\Search\AbstractRegexGambit;
-use Flarum\Search\AbstractSearch;
-use LogicException;
-
-class HiddenGambit extends AbstractRegexGambit
-{
-    /**
-     * {@inheritdoc}
-     */
-    protected $pattern = 'is:hidden';
-
-    /**
-     * {@inheritdoc}
-     */
-    protected function conditions(AbstractSearch $search, array $matches, $negate)
-    {
-        if (! $search instanceof DiscussionSearch) {
-            throw new LogicException('This gambit can only be applied on a DiscussionSearch');
-        }
-
-        $search->getQuery()->where(function ($query) use ($negate) {
-            if ($negate) {
-                $query->whereNull('hidden_at')->where('comment_count', '>', 0);
-            } else {
-                $query->whereNotNull('hidden_at')->orWhere('comment_count', 0);
-            }
-        });
-    }
-}
diff --git a/src/Extend/Filter.php b/src/Extend/Filter.php
new file mode 100644
index 000000000..49f54c541
--- /dev/null
+++ b/src/Extend/Filter.php
@@ -0,0 +1,74 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Flarum\Extension\Extension;
+use Illuminate\Contracts\Container\Container;
+
+class Filter implements ExtenderInterface
+{
+    private $filtererClass;
+    private $filters = [];
+    private $filterMutators = [];
+
+    /**
+     * @param string $filtererClass: The ::class attribute of the filterer to extend
+     */
+    public function __construct($filtererClass)
+    {
+        $this->filtererClass = $filtererClass;
+    }
+
+    /**
+     * Add a filter to run when the filtererClass is filtered.
+     *
+     * @param string $filterClass: The ::class attribute of the filter you are adding.
+     */
+    public function addFilter(string $filterClass)
+    {
+        $this->filters[] = $filterClass;
+
+        return $this;
+    }
+
+    /**
+     * Add a callback through which to run all filter queries after filters have been applied.
+     *
+     * @param callable|string $callback
+     *
+     * The callback can be a closure or an invokable class, and should accept:
+     * - Flarum\Filter\FilterState $filter
+     * - Flarum\Search\SearchCriteria $criteria
+     */
+    public function addFilterMutator($callback)
+    {
+        $this->filterMutators[] = $callback;
+
+        return $this;
+    }
+
+    public function extend(Container $container, Extension $extension = null)
+    {
+        $container->extend('flarum.filter.filters', function ($originalFilters) {
+            foreach ($this->filters as $filter) {
+                $originalFilters[$this->filtererClass][] = $filter;
+            }
+
+            return $originalFilters;
+        });
+        $container->extend('flarum.filter.filter_mutators', function ($originalMutators) {
+            foreach ($this->filterMutators as $mutator) {
+                $originalMutators[$this->filtererClass][] = $mutator;
+            }
+
+            return $originalMutators;
+        });
+    }
+}
diff --git a/src/Extend/SimpleFlarumSearch.php b/src/Extend/SimpleFlarumSearch.php
index 6f308a506..678ed6754 100644
--- a/src/Extend/SimpleFlarumSearch.php
+++ b/src/Extend/SimpleFlarumSearch.php
@@ -60,7 +60,7 @@ class SimpleFlarumSearch implements ExtenderInterface
      * @param callable|string $callback
      *
      * The callback can be a closure or an invokable class, and should accept:
-     * - Flarum\Search\AbstractSearch $search
+     * - Flarum\Search\SearchState $search
      * - Flarum\Search\SearchCriteria $criteria
      */
     public function addSearchMutator($callback)
diff --git a/src/Filter/AbstractFilterer.php b/src/Filter/AbstractFilterer.php
new file mode 100644
index 000000000..c7ddc0542
--- /dev/null
+++ b/src/Filter/AbstractFilterer.php
@@ -0,0 +1,86 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Filter;
+
+use Flarum\Search\ApplySearchParametersTrait;
+use Flarum\Search\SearchCriteria;
+use Flarum\Search\SearchResults;
+use Flarum\User\User;
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Support\Arr;
+use InvalidArgumentException;
+
+abstract class AbstractFilterer
+{
+    use ApplySearchParametersTrait;
+
+    protected $filters;
+
+    protected $filterMutators;
+
+    /**
+     * @param array $filters
+     * @param array $filterMutators
+     */
+    public function __construct(array $filters, array $filterMutators)
+    {
+        $this->filters = $filters;
+        $this->filterMutators = $filterMutators;
+    }
+
+    abstract protected function getQuery(User $actor): Builder;
+
+    /**
+     * @param SearchCriteria $criteria
+     * @param mixed|null $limit
+     * @param int $offset
+     *
+     * @return SearchResults
+     * @throws InvalidArgumentException
+     */
+    public function filter(SearchCriteria $criteria, int $limit = null, int $offset = 0): SearchResults
+    {
+        $actor = $criteria->actor;
+
+        $query = $this->getQuery($actor);
+
+        $filterState = new FilterState($query->getQuery(), $actor);
+
+        foreach ($criteria->query as $filterKey => $filterValue) {
+            $negate = false;
+            if (substr($filterKey, 0, 1) == '-') {
+                $negate = true;
+                $filterKey = substr($filterKey, 1);
+            }
+            foreach (Arr::get($this->filters, $filterKey, []) as $filter) {
+                $filter->filter($filterState, $filterValue, $negate);
+            }
+        }
+
+        $this->applySort($filterState, $criteria->sort);
+        $this->applyOffset($filterState, $offset);
+        $this->applyLimit($filterState, $limit + 1);
+
+        foreach ($this->filterMutators as $mutator) {
+            $mutator($query, $actor, $criteria->query, $criteria->sort);
+        }
+
+        // Execute the filter query and retrieve the results. We get one more
+        // results than the user asked for, so that we can say if there are more
+        // results. If there are, we will get rid of that extra result.
+        $results = $query->get();
+
+        if ($areMoreResults = $limit > 0 && $results->count() > $limit) {
+            $results->pop();
+        }
+
+        return new SearchResults($results, $areMoreResults);
+    }
+}
diff --git a/src/Filter/FilterInterface.php b/src/Filter/FilterInterface.php
new file mode 100644
index 000000000..a5853c4bd
--- /dev/null
+++ b/src/Filter/FilterInterface.php
@@ -0,0 +1,26 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Filter;
+
+interface FilterInterface
+{
+    /**
+     * This filter will only be run when a query contains a filter param with this key.
+     */
+    public function getFilterKey(): string;
+
+    /**
+     * Filters a query.
+     *
+     * @param FilterState $filter
+     * @param string $value The value of the requested filter
+     */
+    public function filter(FilterState $filterState, string $filterValue, bool $negate);
+}
diff --git a/src/Filter/FilterServiceProvider.php b/src/Filter/FilterServiceProvider.php
new file mode 100644
index 000000000..477ea7a30
--- /dev/null
+++ b/src/Filter/FilterServiceProvider.php
@@ -0,0 +1,85 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Filter;
+
+use Flarum\Discussion\Filter\AuthorFilterGambit;
+use Flarum\Discussion\Filter\CreatedFilterGambit;
+use Flarum\Discussion\Filter\DiscussionFilterer;
+use Flarum\Discussion\Filter\HiddenFilterGambit;
+use Flarum\Discussion\Filter\UnreadFilterGambit;
+use Flarum\Foundation\AbstractServiceProvider;
+use Flarum\Foundation\ContainerUtil;
+use Flarum\User\Filter\EmailFilterGambit;
+use Flarum\User\Filter\GroupFilterGambit;
+use Flarum\User\Filter\UserFilterer;
+use Illuminate\Support\Arr;
+
+class FilterServiceProvider extends AbstractServiceProvider
+{
+    /**
+     * Register the service provider.
+     *
+     * @return void
+     */
+    public function register()
+    {
+        $this->app->singleton('flarum.filter.filters', function () {
+            return [
+                DiscussionFilterer::class => [
+                    AuthorFilterGambit::class,
+                    CreatedFilterGambit::class,
+                    HiddenFilterGambit::class,
+                    UnreadFilterGambit::class,
+                ],
+                UserFilterer::class => [
+                    EmailFilterGambit::class,
+                    GroupFilterGambit::class,
+                ]
+            ];
+        });
+
+        $this->app->singleton('flarum.filter.filter_mutators', function () {
+            return [];
+        });
+    }
+
+    public function boot()
+    {
+        // We can resolve the filter mutators in the when->needs->give callback,
+        // but we need to resolve at least one regardless so we know which
+        // filterers we need to register filters for.
+        $filters = $this->app->make('flarum.filter.filters');
+
+        foreach ($filters as $filterer => $filterClasses) {
+            $this->app
+                ->when($filterer)
+                ->needs('$filters')
+                ->give(function () use ($filterClasses) {
+                    $compiled = [];
+
+                    foreach ($filterClasses as $filterClass) {
+                        $filter = $this->app->make($filterClass);
+                        $compiled[$filter->getFilterKey()][] = $filter;
+                    }
+
+                    return $compiled;
+                });
+
+            $this->app
+                ->when($filterer)
+                ->needs('$filterMutators')
+                ->give(function () use ($filterer) {
+                    return array_map(function ($filterMutatorClass) {
+                        return ContainerUtil::wrapCallback($filterMutatorClass, $this->app);
+                    }, Arr::get($this->app->make('flarum.filter.filter_mutators'), $filterer, []));
+                });
+        }
+    }
+}
diff --git a/src/Filter/FilterState.php b/src/Filter/FilterState.php
new file mode 100644
index 000000000..cc5a4a259
--- /dev/null
+++ b/src/Filter/FilterState.php
@@ -0,0 +1,87 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Filter;
+
+use Flarum\User\User;
+use Illuminate\Database\Query\Builder;
+
+class FilterState
+{
+    /**
+     * @var Builder
+     */
+    protected $query;
+
+    /**
+     * @var User
+     */
+    protected $actor;
+
+    /**
+     * @var mixed
+     */
+    protected $defaultSort = [];
+
+    /**
+     * @param Builder $query
+     * @param User $actor
+     */
+    public function __construct(Builder $query, User $actor, $defaultSort = [])
+    {
+        $this->query = $query;
+        $this->actor = $actor;
+        $this->defaultSort = $defaultSort;
+    }
+
+    /**
+     * Get the query builder for the search results query.
+     *
+     * @return Builder
+     */
+    public function getQuery()
+    {
+        return $this->query;
+    }
+
+    /**
+     * Get the user who is performing the search.
+     *
+     * @return User
+     */
+    public function getActor()
+    {
+        return $this->actor;
+    }
+
+    /**
+     * Get the default sort order for the search.
+     *
+     * @return array
+     */
+    public function getDefaultSort()
+    {
+        return $this->defaultSort;
+    }
+
+    /**
+     * Set the default sort order for the search. This will only be applied if
+     * a sort order has not been specified in the search criteria.
+     *
+     * @param mixed $defaultSort An array of sort-order pairs, where the column
+     *     is the key, and the order is the value. The order may be 'asc',
+     *     'desc', or an array of IDs to order by.
+     *     Alternatively, a callable may be used.
+     * @return mixed
+     */
+    public function setDefaultSort($defaultSort)
+    {
+        $this->defaultSort = $defaultSort;
+    }
+}
diff --git a/src/Foundation/InstalledSite.php b/src/Foundation/InstalledSite.php
index 8e944e827..ec52fb9cc 100644
--- a/src/Foundation/InstalledSite.php
+++ b/src/Foundation/InstalledSite.php
@@ -16,6 +16,7 @@ use Flarum\Console\ConsoleServiceProvider;
 use Flarum\Database\DatabaseServiceProvider;
 use Flarum\Discussion\DiscussionServiceProvider;
 use Flarum\Extension\ExtensionServiceProvider;
+use Flarum\Filter\FilterServiceProvider;
 use Flarum\Formatter\FormatterServiceProvider;
 use Flarum\Forum\ForumServiceProvider;
 use Flarum\Frontend\FrontendServiceProvider;
@@ -117,6 +118,7 @@ class InstalledSite implements SiteInterface
         $laravel->register(ExtensionServiceProvider::class);
         $laravel->register(ErrorServiceProvider::class);
         $laravel->register(FilesystemServiceProvider::class);
+        $laravel->register(FilterServiceProvider::class);
         $laravel->register(FormatterServiceProvider::class);
         $laravel->register(ForumServiceProvider::class);
         $laravel->register(FrontendServiceProvider::class);
diff --git a/src/Search/AbstractRegexGambit.php b/src/Search/AbstractRegexGambit.php
index 204b05c32..c1dd0fc2c 100644
--- a/src/Search/AbstractRegexGambit.php
+++ b/src/Search/AbstractRegexGambit.php
@@ -13,15 +13,15 @@ abstract class AbstractRegexGambit implements GambitInterface
 {
     /**
      * The regex pattern to match the bit against.
-     *
-     * @var string
      */
-    protected $pattern;
+    protected function getGambitPattern()
+    {
+    }
 
     /**
      * {@inheritdoc}
      */
-    public function apply(AbstractSearch $search, $bit)
+    public function apply(SearchState $search, $bit)
     {
         if ($matches = $this->match($bit)) {
             list($negate) = array_splice($matches, 1, 1);
@@ -40,7 +40,8 @@ abstract class AbstractRegexGambit implements GambitInterface
      */
     protected function match($bit)
     {
-        if (preg_match('/^(-?)'.$this->pattern.'$/i', $bit, $matches)) {
+        // @deprecated, remove use of $this->pattern during beta 17.
+        if (preg_match('/^(-?)'.($this->pattern ?? $this->getGambitPattern()).'$/i', $bit, $matches)) {
             return $matches;
         }
     }
@@ -48,11 +49,12 @@ abstract class AbstractRegexGambit implements GambitInterface
     /**
      * Apply conditions to the search, given that the gambit was matched.
      *
-     * @param AbstractSearch $search The search object.
+     * @param SearchState $search The search object.
      * @param array $matches An array of matches from the search bit.
      * @param bool $negate Whether or not the bit was negated, and thus whether
      *     or not the conditions should be negated.
      * @return mixed
      */
-    abstract protected function conditions(AbstractSearch $search, array $matches, $negate);
+    // Uncomment for beta 17
+    // abstract protected function conditions(SearchState $search, array $matches, $negate);
 }
diff --git a/src/Search/AbstractSearch.php b/src/Search/AbstractSearch.php
index 1de7dcac9..adac8ceb2 100644
--- a/src/Search/AbstractSearch.php
+++ b/src/Search/AbstractSearch.php
@@ -9,90 +9,19 @@
 
 namespace Flarum\Search;
 
-use Flarum\User\User;
-use Illuminate\Database\Query\Builder;
+use Flarum\Filter\FilterState;
 
 /**
- * An object which represents the internal state of a generic search:
- * the search query, the user performing the search, the fallback sort order,
- * and a log of which gambits have been used.
+ * @deprecated, use SearchState instead.
+ * These methods should be transferred over to SearchState in beta 17.
  */
-abstract class AbstractSearch
+class AbstractSearch extends FilterState
 {
-    /**
-     * @var Builder
-     */
-    protected $query;
-
-    /**
-     * @var User
-     */
-    protected $actor;
-
-    /**
-     * @var array
-     */
-    protected $defaultSort = [];
-
     /**
      * @var GambitInterface[]
      */
     protected $activeGambits = [];
 
-    /**
-     * @param Builder $query
-     * @param User $actor
-     */
-    public function __construct(Builder $query, User $actor)
-    {
-        $this->query = $query;
-        $this->actor = $actor;
-    }
-
-    /**
-     * Get the query builder for the search results query.
-     *
-     * @return Builder
-     */
-    public function getQuery()
-    {
-        return $this->query;
-    }
-
-    /**
-     * Get the user who is performing the search.
-     *
-     * @return User
-     */
-    public function getActor()
-    {
-        return $this->actor;
-    }
-
-    /**
-     * Get the default sort order for the search.
-     *
-     * @return array
-     */
-    public function getDefaultSort()
-    {
-        return $this->defaultSort;
-    }
-
-    /**
-     * Set the default sort order for the search. This will only be applied if
-     * a sort order has not been specified in the search criteria.
-     *
-     * @param mixed $defaultSort An array of sort-order pairs, where the column
-     *     is the key, and the order is the value. The order may be 'asc',
-     *     'desc', or an array of IDs to order by.
-     * @return mixed
-     */
-    public function setDefaultSort($defaultSort)
-    {
-        $this->defaultSort = $defaultSort;
-    }
-
     /**
      * Get a list of the gambits that are active in this search.
      *
diff --git a/src/Search/AbstractSearcher.php b/src/Search/AbstractSearcher.php
index 9ccb33d59..58de86243 100644
--- a/src/Search/AbstractSearcher.php
+++ b/src/Search/AbstractSearcher.php
@@ -34,9 +34,7 @@ abstract class AbstractSearcher
 
     abstract protected function getQuery(User $actor): Builder;
 
-    abstract protected function getSearch(Builder $query, User $actor): AbstractSearch;
-
-    protected function mutateSearch(AbstractSearch $search, SearchCriteria $criteria)
+    protected function mutateSearch(SearchState $search, SearchCriteria $criteria)
     {
         foreach ($this->searchMutators as $mutator) {
             $mutator($search, $criteria);
@@ -49,16 +47,17 @@ abstract class AbstractSearcher
      * @param int $offset
      *
      * @return SearchResults
+     * @throws InvalidArgumentException
      */
-    public function search(SearchCriteria $criteria, $limit = null, $offset = 0, array $load = [])
+    public function search(SearchCriteria $criteria, $limit = null, $offset = 0): SearchResults
     {
         $actor = $criteria->actor;
 
         $query = $this->getQuery($actor);
 
-        $search = $this->getSearch($query, $actor);
+        $search = new SearchState($query->getQuery(), $actor);
 
-        $this->gambits->apply($search, $criteria->query);
+        $this->gambits->apply($search, $criteria->query['q']);
         $this->applySort($search, $criteria->sort);
         $this->applyOffset($search, $offset);
         $this->applyLimit($search, $limit + 1);
@@ -74,8 +73,6 @@ abstract class AbstractSearcher
             $results->pop();
         }
 
-        $results->load($load);
-
         return new SearchResults($results, $areMoreResults);
     }
 }
diff --git a/src/Search/ApplySearchParametersTrait.php b/src/Search/ApplySearchParametersTrait.php
index 0e5798743..2b77a5bd8 100644
--- a/src/Search/ApplySearchParametersTrait.php
+++ b/src/Search/ApplySearchParametersTrait.php
@@ -9,6 +9,7 @@
 
 namespace Flarum\Search;
 
+use Flarum\Filter\FilterState;
 use Illuminate\Support\Str;
 
 trait ApplySearchParametersTrait
@@ -16,10 +17,10 @@ trait ApplySearchParametersTrait
     /**
      * Apply sort criteria to a discussion search.
      *
-     * @param AbstractSearch $search
+     * @param FilterState $search
      * @param array $sort
      */
-    protected function applySort(AbstractSearch $search, array $sort = null)
+    protected function applySort(FilterState $search, array $sort = null)
     {
         $sort = $sort ?: $search->getDefaultSort();
 
@@ -39,10 +40,10 @@ trait ApplySearchParametersTrait
     }
 
     /**
-     * @param AbstractSearch $search
+     * @param FilterState $search
      * @param int $offset
      */
-    protected function applyOffset(AbstractSearch $search, $offset)
+    protected function applyOffset(FilterState $search, $offset)
     {
         if ($offset > 0) {
             $search->getQuery()->skip($offset);
@@ -50,10 +51,10 @@ trait ApplySearchParametersTrait
     }
 
     /**
-     * @param AbstractSearch $search
+     * @param FilterState $search
      * @param int|null $limit
      */
-    protected function applyLimit(AbstractSearch $search, $limit)
+    protected function applyLimit(FilterState $search, $limit)
     {
         if ($limit > 0) {
             $search->getQuery()->take($limit);
diff --git a/src/Search/GambitInterface.php b/src/Search/GambitInterface.php
index 4a190a2c8..cbb691e63 100644
--- a/src/Search/GambitInterface.php
+++ b/src/Search/GambitInterface.php
@@ -14,9 +14,9 @@ interface GambitInterface
     /**
      * Apply conditions to the searcher for a bit of the search string.
      *
-     * @param AbstractSearch $search
+     * @param SearchState $search
      * @param string $bit The piece of the search string.
      * @return bool Whether or not the gambit was active for this bit.
      */
-    public function apply(AbstractSearch $search, $bit);
+    public function apply(SearchState $search, $bit);
 }
diff --git a/src/Search/GambitManager.php b/src/Search/GambitManager.php
index 775af42b6..b9e5b0b0f 100644
--- a/src/Search/GambitManager.php
+++ b/src/Search/GambitManager.php
@@ -55,10 +55,10 @@ class GambitManager
     /**
      * Apply gambits to a search, given a search query.
      *
-     * @param AbstractSearch $search
+     * @param SearchState $search
      * @param string $query
      */
-    public function apply(AbstractSearch $search, $query)
+    public function apply(SearchState $search, $query)
     {
         $query = $this->applyGambits($search, $query);
 
@@ -89,11 +89,11 @@ class GambitManager
     }
 
     /**
-     * @param AbstractSearch $search
+     * @param SearchState $search
      * @param string $query
      * @return string
      */
-    protected function applyGambits(AbstractSearch $search, $query)
+    protected function applyGambits(SearchState $search, $query)
     {
         $bits = $this->explode($query);
 
@@ -121,10 +121,10 @@ class GambitManager
     }
 
     /**
-     * @param AbstractSearch $search
+     * @param SearchState $search
      * @param string $query
      */
-    protected function applyFulltext(AbstractSearch $search, $query)
+    protected function applyFulltext(SearchState $search, $query)
     {
         if (! $this->fulltextGambit) {
             return;
diff --git a/src/Search/SearchCriteria.php b/src/Search/SearchCriteria.php
index 6e8dd6e36..30820dd67 100644
--- a/src/Search/SearchCriteria.php
+++ b/src/Search/SearchCriteria.php
@@ -13,22 +13,22 @@ use Flarum\User\User;
 
 /**
  * Represents the criteria that will determine the entire result set of a
- * search. The limit and offset are not included because they only determine
+ * query. The limit and offset are not included because they only determine
  * which part of the entire result set will be returned.
  */
 class SearchCriteria
 {
     /**
-     * The user performing the search.
+     * The user performing the query.
      *
      * @var User
      */
     public $actor;
 
     /**
-     * The search query.
+     * Query params.
      *
-     * @var string
+     * @var array
      */
     public $query;
 
@@ -42,8 +42,8 @@ class SearchCriteria
     public $sort;
 
     /**
-     * @param User $actor The user performing the search.
-     * @param string $query The search query.
+     * @param User $actor The user performing the query.
+     * @param array $query The query params.
      * @param array $sort An array of sort-order pairs, where the column is the
      *     key, and the order is the value. The order may be 'asc', 'desc', or
      *     an array of IDs to order by.
diff --git a/src/Search/SearchServiceProvider.php b/src/Search/SearchServiceProvider.php
index fee38bf95..264958f92 100644
--- a/src/Search/SearchServiceProvider.php
+++ b/src/Search/SearchServiceProvider.php
@@ -9,19 +9,19 @@
 
 namespace Flarum\Search;
 
+use Flarum\Discussion\Filter\AuthorFilterGambit;
+use Flarum\Discussion\Filter\CreatedFilterGambit;
+use Flarum\Discussion\Filter\HiddenFilterGambit;
+use Flarum\Discussion\Filter\UnreadFilterGambit;
 use Flarum\Discussion\Search\DiscussionSearcher;
-use Flarum\Discussion\Search\Gambit\AuthorGambit;
-use Flarum\Discussion\Search\Gambit\CreatedGambit;
 use Flarum\Discussion\Search\Gambit\FulltextGambit as DiscussionFulltextGambit;
-use Flarum\Discussion\Search\Gambit\HiddenGambit;
-use Flarum\Discussion\Search\Gambit\UnreadGambit;
 use Flarum\Event\ConfigureDiscussionGambits;
 use Flarum\Event\ConfigureUserGambits;
 use Flarum\Foundation\AbstractServiceProvider;
 use Flarum\Foundation\ContainerUtil;
-use Flarum\User\Search\Gambit\EmailGambit;
+use Flarum\User\Filter\EmailFilterGambit;
+use Flarum\User\Filter\GroupFilterGambit;
 use Flarum\User\Search\Gambit\FulltextGambit as UserFulltextGambit;
-use Flarum\User\Search\Gambit\GroupGambit;
 use Flarum\User\Search\UserSearcher;
 use Illuminate\Support\Arr;
 
@@ -42,14 +42,14 @@ class SearchServiceProvider extends AbstractServiceProvider
         $this->app->singleton('flarum.simple_search.gambits', function () {
             return [
                 DiscussionSearcher::class => [
-                    AuthorGambit::class,
-                    CreatedGambit::class,
-                    HiddenGambit::class,
-                    UnreadGambit::class
+                    AuthorFilterGambit::class,
+                    CreatedFilterGambit::class,
+                    HiddenFilterGambit::class,
+                    UnreadFilterGambit::class
                 ],
                 UserSearcher::class => [
-                    EmailGambit::class,
-                    GroupGambit::class
+                    EmailFilterGambit::class,
+                    GroupFilterGambit::class
                 ]
             ];
         });
diff --git a/src/User/Search/UserSearch.php b/src/Search/SearchState.php
similarity index 63%
rename from src/User/Search/UserSearch.php
rename to src/Search/SearchState.php
index 37106e538..b57fbeee2 100644
--- a/src/User/Search/UserSearch.php
+++ b/src/Search/SearchState.php
@@ -7,10 +7,8 @@
  * LICENSE file that was distributed with this source code.
  */
 
-namespace Flarum\User\Search;
+namespace Flarum\Search;
 
-use Flarum\Search\AbstractSearch;
-
-class UserSearch extends AbstractSearch
+class SearchState extends AbstractSearch
 {
 }
diff --git a/src/User/Event/Searching.php b/src/User/Event/Searching.php
index ffa0db36c..ff6debac7 100644
--- a/src/User/Event/Searching.php
+++ b/src/User/Event/Searching.php
@@ -10,7 +10,7 @@
 namespace Flarum\User\Event;
 
 use Flarum\Search\SearchCriteria;
-use Flarum\User\Search\UserSearch;
+use Flarum\Search\SearchState;
 
 /**
  * @deprecated beta 16, remove beta 17
@@ -18,7 +18,7 @@ use Flarum\User\Search\UserSearch;
 class Searching
 {
     /**
-     * @var \Flarum\User\Search\UserSearch
+     * @var \Flarum\User\Search\SearchState
      */
     public $search;
 
@@ -28,10 +28,10 @@ class Searching
     public $criteria;
 
     /**
-     * @param UserSearch $search
+     * @param SearchState $search
      * @param SearchCriteria $criteria
      */
-    public function __construct(UserSearch $search, SearchCriteria $criteria)
+    public function __construct(SearchState $search, SearchCriteria $criteria)
     {
         $this->search = $search;
         $this->criteria = $criteria;
diff --git a/src/User/Filter/EmailFilterGambit.php b/src/User/Filter/EmailFilterGambit.php
new file mode 100644
index 000000000..3fc4ae9ab
--- /dev/null
+++ b/src/User/Filter/EmailFilterGambit.php
@@ -0,0 +1,68 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\User\Filter;
+
+use Flarum\Filter\FilterInterface;
+use Flarum\Filter\FilterState;
+use Flarum\Search\AbstractRegexGambit;
+use Flarum\Search\SearchState;
+use Illuminate\Database\Query\Builder;
+
+class EmailFilterGambit extends AbstractRegexGambit implements FilterInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function apply(SearchState $search, $bit)
+    {
+        if (! $search->getActor()->hasPermission('user.edit')) {
+            return false;
+        }
+
+        return parent::apply($search, $bit);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getGambitPattern()
+    {
+        return 'email:(.+)';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function conditions(SearchState $search, array $matches, $negate)
+    {
+        $this->constrain($search->getQuery(), $matches[1], $negate);
+    }
+
+    public function getFilterKey(): string
+    {
+        return 'email';
+    }
+
+    public function filter(FilterState $filterState, string $filterValue, bool $negate)
+    {
+        if (! $filterState->getActor()->hasPermission('user.edit')) {
+            return;
+        }
+
+        $this->constrain($filterState->getQuery(), $filterValue, $negate);
+    }
+
+    protected function constrain(Builder $query, $rawEmail, bool $negate)
+    {
+        $email = trim($rawEmail, '"');
+
+        $query->where('email', $negate ? '!=' : '=', $email);
+    }
+}
diff --git a/src/User/Filter/GroupFilterGambit.php b/src/User/Filter/GroupFilterGambit.php
new file mode 100644
index 000000000..4d1c445f8
--- /dev/null
+++ b/src/User/Filter/GroupFilterGambit.php
@@ -0,0 +1,68 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\User\Filter;
+
+use Flarum\Filter\FilterInterface;
+use Flarum\Filter\FilterState;
+use Flarum\Group\Group;
+use Flarum\Search\AbstractRegexGambit;
+use Flarum\Search\SearchState;
+use Flarum\User\User;
+use Illuminate\Database\Query\Builder;
+
+class GroupFilterGambit extends AbstractRegexGambit implements FilterInterface
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function getGambitPattern()
+    {
+        return 'group:(.+)';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function conditions(SearchState $search, array $matches, $negate)
+    {
+        $this->constrain($search->getQuery(), $search->getActor(), $matches[1], $negate);
+    }
+
+    public function getFilterKey(): string
+    {
+        return 'group';
+    }
+
+    public function filter(FilterState $filterState, string $filterValue, bool $negate)
+    {
+        $this->constrain($filterState->getQuery(), $filterState->getActor(), $filterValue, $negate);
+    }
+
+    protected function constrain(Builder $query, User $actor, string $rawQuery, bool $negate)
+    {
+        $groupIdentifiers = explode(',', trim($rawQuery, '"'));
+
+        $groupQuery = Group::whereVisibleTo($actor);
+
+        foreach ($groupIdentifiers as $identifier) {
+            if (is_numeric($identifier)) {
+                $groupQuery->orWhere('id', $identifier);
+            } else {
+                $groupQuery->orWhere('name_singular', $identifier)->orWhere('name_plural', $identifier);
+            }
+        }
+
+        $userIds = $groupQuery->join('group_user', 'groups.id', 'group_user.group_id')
+            ->pluck('group_user.user_id')
+            ->all();
+
+        $query->whereIn('id', $userIds, 'and', $negate);
+    }
+}
diff --git a/src/User/Filter/UserFilterer.php b/src/User/Filter/UserFilterer.php
new file mode 100644
index 000000000..418dca379
--- /dev/null
+++ b/src/User/Filter/UserFilterer.php
@@ -0,0 +1,40 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\User\Filter;
+
+use Flarum\Filter\AbstractFilterer;
+use Flarum\User\User;
+use Flarum\User\UserRepository;
+use Illuminate\Database\Eloquent\Builder;
+
+class UserFilterer extends AbstractFilterer
+{
+    /**
+     * @var UserRepository
+     */
+    protected $users;
+
+    /**
+     * @param UserRepository $users
+     * @param array $filters
+     * @param array $filterMutators
+     */
+    public function __construct(UserRepository $users, array $filters, array $filterMutators)
+    {
+        parent::__construct($filters, $filterMutators);
+
+        $this->users = $users;
+    }
+
+    protected function getQuery(User $actor): Builder
+    {
+        return $this->users->query()->whereVisibleTo($actor);
+    }
+}
diff --git a/src/User/Search/Gambit/EmailGambit.php b/src/User/Search/Gambit/EmailGambit.php
deleted file mode 100644
index f3ca088b6..000000000
--- a/src/User/Search/Gambit/EmailGambit.php
+++ /dev/null
@@ -1,63 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\User\Search\Gambit;
-
-use Flarum\Search\AbstractRegexGambit;
-use Flarum\Search\AbstractSearch;
-use Flarum\User\Search\UserSearch;
-use Flarum\User\UserRepository;
-use LogicException;
-
-class EmailGambit extends AbstractRegexGambit
-{
-    /**
-     * {@inheritdoc}
-     */
-    protected $pattern = 'email:(.+)';
-
-    /**
-     * @var \Flarum\User\UserRepository
-     */
-    protected $users;
-
-    /**
-     * @param \Flarum\User\UserRepository $users
-     */
-    public function __construct(UserRepository $users)
-    {
-        $this->users = $users;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    public function apply(AbstractSearch $search, $bit)
-    {
-        if (! $search->getActor()->hasPermission('user.edit')) {
-            return false;
-        }
-
-        return parent::apply($search, $bit);
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    protected function conditions(AbstractSearch $search, array $matches, $negate)
-    {
-        if (! $search instanceof UserSearch) {
-            throw new LogicException('This gambit can only be applied on a UserSearch');
-        }
-
-        $email = trim($matches[1], '"');
-
-        $search->getQuery()->where('email', $negate ? '!=' : '=', $email);
-    }
-}
diff --git a/src/User/Search/Gambit/FulltextGambit.php b/src/User/Search/Gambit/FulltextGambit.php
index 410d74810..0522e76d2 100644
--- a/src/User/Search/Gambit/FulltextGambit.php
+++ b/src/User/Search/Gambit/FulltextGambit.php
@@ -9,8 +9,8 @@
 
 namespace Flarum\User\Search\Gambit;
 
-use Flarum\Search\AbstractSearch;
 use Flarum\Search\GambitInterface;
+use Flarum\Search\SearchState;
 use Flarum\User\UserRepository;
 
 class FulltextGambit implements GambitInterface
@@ -43,7 +43,7 @@ class FulltextGambit implements GambitInterface
     /**
      * {@inheritdoc}
      */
-    public function apply(AbstractSearch $search, $searchValue)
+    public function apply(SearchState $search, $searchValue)
     {
         $search->getQuery()
             ->whereIn(
diff --git a/src/User/Search/Gambit/GroupGambit.php b/src/User/Search/Gambit/GroupGambit.php
deleted file mode 100644
index 5e113e6df..000000000
--- a/src/User/Search/Gambit/GroupGambit.php
+++ /dev/null
@@ -1,77 +0,0 @@
-<?php
-
-/*
- * This file is part of Flarum.
- *
- * For detailed copyright and license information, please view the
- * LICENSE file that was distributed with this source code.
- */
-
-namespace Flarum\User\Search\Gambit;
-
-use Flarum\Group\Group;
-use Flarum\Group\GroupRepository;
-use Flarum\Search\AbstractRegexGambit;
-use Flarum\Search\AbstractSearch;
-use Flarum\User\Search\UserSearch;
-use LogicException;
-
-class GroupGambit extends AbstractRegexGambit
-{
-    /**
-     * {@inheritdoc}
-     */
-    protected $pattern = 'group:(.+)';
-
-    /**
-     * @var GroupRepository
-     */
-    protected $groups;
-
-    /**
-     * @param \Flarum\Group\GroupRepository $groups
-     */
-    public function __construct(GroupRepository $groups)
-    {
-        $this->groups = $groups;
-    }
-
-    /**
-     * {@inheritdoc}
-     */
-    protected function conditions(AbstractSearch $search, array $matches, $negate)
-    {
-        if (! $search instanceof UserSearch) {
-            throw new LogicException('This gambit can only be applied on a UserSearch');
-        }
-
-        $groupIdentifiers = $this->extractGroupIdentifiers($matches);
-
-        $groupQuery = Group::whereVisibleTo($search->getActor());
-
-        foreach ($groupIdentifiers as $identifier) {
-            if (is_numeric($identifier)) {
-                $groupQuery->orWhere('id', $identifier);
-            } else {
-                $groupQuery->orWhere('name_singular', $identifier)->orWhere('name_plural', $identifier);
-            }
-        }
-
-        $userIds = $groupQuery->join('group_user', 'groups.id', 'group_user.group_id')
-            ->pluck('group_user.user_id')
-            ->all();
-
-        $search->getQuery()->whereIn('id', $userIds, 'and', $negate);
-    }
-
-    /**
-     * Extract the group names from the pattern match.
-     *
-     * @param array $matches
-     * @return array
-     */
-    protected function extractGroupIdentifiers(array $matches)
-    {
-        return explode(',', trim($matches[1], '"'));
-    }
-}
diff --git a/src/User/Search/UserSearcher.php b/src/User/Search/UserSearcher.php
index cecd75651..d0ac09970 100644
--- a/src/User/Search/UserSearcher.php
+++ b/src/User/Search/UserSearcher.php
@@ -9,10 +9,10 @@
 
 namespace Flarum\User\Search;
 
-use Flarum\Search\AbstractSearch;
 use Flarum\Search\AbstractSearcher;
 use Flarum\Search\GambitManager;
 use Flarum\Search\SearchCriteria;
+use Flarum\Search\SearchState;
 use Flarum\User\Event\Searching;
 use Flarum\User\User;
 use Flarum\User\UserRepository;
@@ -54,15 +54,10 @@ class UserSearcher extends AbstractSearcher
         return $this->users->query()->whereVisibleTo($actor);
     }
 
-    protected function getSearch(Builder $query, User $actor): AbstractSearch
-    {
-        return new UserSearch($query->getQuery(), $actor);
-    }
-
     /**
      * @deprecated along with the Searching event, remove in Beta 17.
      */
-    protected function mutateSearch(AbstractSearch $search, SearchCriteria $criteria)
+    protected function mutateSearch(SearchState $search, SearchCriteria $criteria)
     {
         parent::mutateSearch($search, $criteria);
 
diff --git a/tests/integration/api/discussions/ListTest.php b/tests/integration/api/discussions/ListTest.php
index 48e1ee949..9a16f411f 100644
--- a/tests/integration/api/discussions/ListTest.php
+++ b/tests/integration/api/discussions/ListTest.php
@@ -12,6 +12,8 @@ namespace Flarum\Tests\integration\api\discussions;
 use Carbon\Carbon;
 use Flarum\Tests\integration\RetrievesAuthorizedUsers;
 use Flarum\Tests\integration\TestCase;
+use Flarum\User\User;
+use Illuminate\Support\Arr;
 
 class ListTest extends TestCase
 {
@@ -26,10 +28,16 @@ class ListTest extends TestCase
 
         $this->prepareDatabase([
             'discussions' => [
-                ['id' => 1, 'title' => __CLASS__, 'created_at' => Carbon::now()->toDateTimeString(), 'user_id' => 2, 'first_post_id' => 1, 'comment_count' => 1],
+                ['id' => 1, 'title' => __CLASS__, 'created_at' => Carbon::createFromDate(1975, 5, 21)->toDateTimeString(), 'last_posted_at' => Carbon::createFromDate(1975, 5, 21)->toDateTimeString(), 'user_id' => 1, 'first_post_id' => 1, 'comment_count' => 1],
+                ['id' => 2, 'title' => 'lightsail in title', 'created_at' => Carbon::createFromDate(1985, 5, 21)->toDateTimeString(), 'last_posted_at' => Carbon::createFromDate(1985, 5, 21)->toDateTimeString(), 'user_id' => 2, 'comment_count' => 1],
+                ['id' => 3, 'title' => 'not in title', 'created_at' => Carbon::createFromDate(1995, 5, 21)->toDateTimeString(), 'last_posted_at' => Carbon::createFromDate(1995, 5, 21)->toDateTimeString(), 'user_id' => 2, 'comment_count' => 1],
+                ['id' => 4, 'title' => 'hidden', 'created_at' => Carbon::createFromDate(2005, 5, 21)->toDateTimeString(), 'last_posted_at' => Carbon::createFromDate(2005, 5, 21)->toDateTimeString(), 'hidden_at' => Carbon::now()->toDateTimeString(), 'user_id' => 1, 'comment_count' => 1],
             ],
             'posts' => [
-                ['id' => 1, 'discussion_id' => 1, 'created_at' => Carbon::now()->toDateTimeString(), 'user_id' => 2, 'type' => 'comment', 'content' => '<t><p>foo bar</p></t>'],
+                ['id' => 1, 'discussion_id' => 1, 'created_at' => Carbon::createFromDate(1975, 5, 21)->toDateTimeString(), 'user_id' => 1, 'type' => 'comment', 'content' => '<t><p>foo bar</p></t>'],
+                ['id' => 2, 'discussion_id' => 2, 'created_at' => Carbon::createFromDate(1985, 5, 21)->toDateTimeString(), 'user_id' => 2, 'type' => 'comment', 'content' => '<t><p>not in text</p></t>'],
+                ['id' => 3, 'discussion_id' => 3, 'created_at' => Carbon::createFromDate(1995, 5, 21)->toDateTimeString(), 'user_id' => 2, 'type' => 'comment', 'content' => '<t><p>lightsail in text</p></t>'],
+                ['id' => 4, 'discussion_id' => 4, 'created_at' => Carbon::createFromDate(2005, 5, 21)->toDateTimeString(), 'user_id' => 1, 'type' => 'comment', 'content' => '<t><p>lightsail in text</p></t>'],
             ],
             'users' => [
                 $this->normalUser(),
@@ -37,6 +45,16 @@ class ListTest extends TestCase
         ]);
     }
 
+    /**
+     * Mark some discussions, but not others, as read to test that filter/gambit.
+     */
+    protected function read()
+    {
+        $user = User::find(2);
+        $user->marked_all_as_read_at = Carbon::createFromDate(1990, 0, 0)->toDateTimeString();
+        $user->save();
+    }
+
     /**
      * @test
      */
@@ -49,22 +67,398 @@ class ListTest extends TestCase
         $this->assertEquals(200, $response->getStatusCode());
         $data = json_decode($response->getBody()->getContents(), true);
 
-        $this->assertEquals(1, count($data['data']));
+        $this->assertEquals(3, count($data['data']));
     }
 
     /**
      * @test
      */
-    public function can_search_for_author()
+    public function author_filter_works()
     {
         $response = $this->send(
             $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['author' => 'normal'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['2', '3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function author_filter_works_negated()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['-author' => 'normal'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function created_filter_works_with_date()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['created' => '1995-05-21'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function created_filter_works_negated_with_date()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['-created' => '1995-05-21'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1', '2'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function created_filter_works_with_range()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['created' => '1980-05-21..2000-05-21'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['2', '3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function created_filter_works_negated_with_range()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['-created' => '1980-05-21..2000-05-21'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function hidden_filter_works()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions', ['authenticatedAs' => 1])
+            ->withQueryParams([
+                'filter' => ['hidden' => ''],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['4'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function hidden_filter_works_negated()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions', ['authenticatedAs' => 1])
+            ->withQueryParams([
+                'filter' => ['-hidden' => ''],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1', '2', '3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function unread_filter_works()
+    {
+        $this->app();
+        $this->read();
+
+        $response = $this->send(
+            $this->request('GET', '/api/discussions', ['authenticatedAs' => 2])
                 ->withQueryParams([
-                    'filter' => ['q' => 'author:normal foo'],
+                    'filter' => ['unread' => ''],
                     'include' => 'mostRelevantPost',
                 ])
         );
 
-        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function unread_filter_works_when_negated()
+    {
+        $this->app();
+        $this->read();
+
+        $response = $this->send(
+            $this->request('GET', '/api/discussions', ['authenticatedAs' => 2])
+                ->withQueryParams([
+                    'filter' => ['-unread' => ''],
+                    'include' => 'mostRelevantPost',
+                ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1', '2'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function author_gambit_works()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['q' => 'author:normal'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['2', '3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function author_gambit_works_negated()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['q' => '-author:normal'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function created_gambit_works_with_date()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['q' => 'created:1995-05-21'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function created_gambit_works_negated_with_date()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['q' => '-created:1995-05-21'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1', '2'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function created_gambit_works_with_range()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['q' => 'created:1980-05-21..2000-05-21'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['2', '3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function created_gambit_works_negated_with_range()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions')
+            ->withQueryParams([
+                'filter' => ['q' => '-created:1980-05-21..2000-05-21'],
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function hidden_gambit_works()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions', ['authenticatedAs' => 1])
+                ->withQueryParams([
+                    'filter' => ['q' => 'is:hidden'],
+                    'include' => 'mostRelevantPost',
+                ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['4'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function hidden_gambit_works_negated()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions', ['authenticatedAs' => 1])
+                ->withQueryParams([
+                    'filter' => ['q' => '-is:hidden'],
+                    'include' => 'mostRelevantPost',
+                ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1', '2', '3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function unread_gambit_works()
+    {
+        $this->app();
+        $this->read();
+
+        $response = $this->send(
+            $this->request('GET', '/api/discussions', ['authenticatedAs' => 2])
+                ->withQueryParams([
+                    'filter' => ['q' => 'is:unread'],
+                    'include' => 'mostRelevantPost',
+                ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['3'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
+    }
+
+    /**
+     * @test
+     */
+    public function unread_gambit_works_when_negated()
+    {
+        $this->app();
+        $this->read();
+
+        $response = $this->send(
+            $this->request('GET', '/api/discussions', ['authenticatedAs' => 2])
+                ->withQueryParams([
+                    'filter' => ['q' => '-is:unread'],
+                    'include' => 'mostRelevantPost',
+                ])
+        );
+
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+
+        // Order-independent comparison
+        $this->assertEquals(['1', '2'], Arr::pluck($data, 'id'), 'IDs do not match', 0.0, 10, true);
     }
 }
diff --git a/tests/integration/api/users/ListTest.php b/tests/integration/api/users/ListTest.php
index c2b05a941..72199e3b4 100644
--- a/tests/integration/api/users/ListTest.php
+++ b/tests/integration/api/users/ListTest.php
@@ -11,11 +11,26 @@ namespace Flarum\Tests\integration\api\users;
 
 use Flarum\Tests\integration\RetrievesAuthorizedUsers;
 use Flarum\Tests\integration\TestCase;
+use Illuminate\Support\Arr;
 
 class ListTest extends TestCase
 {
     use RetrievesAuthorizedUsers;
 
+    /**
+     * @inheritDoc
+     */
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        $this->prepareDatabase([
+            'users' => [
+                $this->normalUser(),
+            ],
+        ]);
+    }
+
     /**
      * @test
      */
@@ -59,4 +74,200 @@ class ListTest extends TestCase
 
         $this->assertEquals(200, $response->getStatusCode());
     }
+
+    /**
+     * @test
+     */
+    public function shows_full_results_without_search_or_filter()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 1,
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['1', '2'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function group_filter_works()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => ['group' => '1'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['1'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function group_filter_works_negated()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => ['-group' => '1'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['2'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function email_filter_works()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => ['email' => 'admin@machine.local'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['1'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function email_filter_works_negated()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => ['-email' => 'admin@machine.local'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['2'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function email_filter_only_works_for_admin()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 2,
+            ])->withQueryParams([
+                'filter' => ['email' => 'admin@machine.local'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['1', '2'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function group_gambit_works()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => ['q' => 'group:1'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['1'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function group_gambit_works_negated()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => ['q' => '-group:1'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['2'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function email_gambit_works()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => ['q' => 'email:admin@machine.local'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['1'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function email_gambit_works_negated()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => ['q' => '-email:admin@machine.local'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals(['2'], Arr::pluck($data, 'id'));
+    }
+
+    /**
+     * @test
+     */
+    public function email_gambit_only_works_for_admin()
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/users', [
+                'authenticatedAs' => 2,
+            ])->withQueryParams([
+                'filter' => ['q' => 'email:admin@machine.local'],
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+        $data = json_decode($response->getBody()->getContents(), true)['data'];
+        $this->assertEquals([], Arr::pluck($data, 'id'));
+    }
 }
diff --git a/tests/integration/extenders/FilterTest.php b/tests/integration/extenders/FilterTest.php
new file mode 100644
index 000000000..68b81bd7e
--- /dev/null
+++ b/tests/integration/extenders/FilterTest.php
@@ -0,0 +1,134 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Tests\integration\extenders;
+
+use Carbon\Carbon;
+use Flarum\Discussion\Filter\DiscussionFilterer;
+use Flarum\Extend;
+use Flarum\Filter\FilterInterface;
+use Flarum\Filter\FilterState;
+use Flarum\Tests\integration\RetrievesAuthorizedUsers;
+use Flarum\Tests\integration\TestCase;
+
+class FilterTest extends TestCase
+{
+    use RetrievesAuthorizedUsers;
+
+    public function prepDb()
+    {
+        $this->prepareDatabase([
+            'discussions' => [
+                ['id' => 1, 'title' => 'DISCUSSION 1', 'created_at' => Carbon::now()->toDateTimeString(), 'user_id' => 2, 'first_post_id' => 1, 'comment_count' => 1],
+                ['id' => 2, 'title' => 'DISCUSSION 2', 'created_at' => Carbon::now()->toDateTimeString(), 'user_id' => 2, 'first_post_id' => 2, 'comment_count' => 1],
+            ],
+            'posts' => [
+                ['id' => 1, 'discussion_id' => 1, 'created_at' => Carbon::now()->toDateTimeString(), 'user_id' => 2, 'type' => 'comment', 'content' => '<t><p>foo bar</p></t>'],
+                ['id' => 2, 'discussion_id' => 2, 'created_at' => Carbon::now()->toDateTimeString(), 'user_id' => 2, 'type' => 'comment', 'content' => '<t><p>foo bar not the same</p></t>'],
+            ],
+            'users' => [
+                $this->normalUser(),
+            ],
+        ]);
+    }
+
+    public function filterDiscussions($filters, $limit = null)
+    {
+        $response = $this->send(
+            $this->request('GET', '/api/discussions', [
+                'authenticatedAs' => 1,
+            ])->withQueryParams([
+                'filter' => $filters,
+                'include' => 'mostRelevantPost',
+            ])
+        );
+
+        return json_decode($response->getBody()->getContents(), true)['data'];
+    }
+
+    /**
+     * @test
+     */
+    public function works_as_expected_with_no_modifications()
+    {
+        $this->prepDb();
+
+        $searchForAll = json_encode($this->filterDiscussions([], 5));
+        $this->assertContains('DISCUSSION 1', $searchForAll);
+        $this->assertContains('DISCUSSION 2', $searchForAll);
+    }
+
+    /**
+     * @test
+     */
+    public function custom_filter_has_effect_if_added()
+    {
+        $this->extend((new Extend\Filter(DiscussionFilterer::class))->addFilter(NoResultFilter::class));
+
+        $this->prepDb();
+
+        $withResultSearch = json_encode($this->filterDiscussions(['noResult' => 0], 5));
+        $this->assertContains('DISCUSSION 1', $withResultSearch);
+        $this->assertContains('DISCUSSION 2', $withResultSearch);
+        $this->assertEquals([], $this->filterDiscussions(['noResult' => 1], 5));
+    }
+
+    /**
+     * @test
+     */
+    public function filter_mutator_has_effect_if_added()
+    {
+        $this->extend((new Extend\Filter(DiscussionFilterer::class))->addFilterMutator(function ($query, $actor, $filters, $sort) {
+            $query->getQuery()->whereRaw('1=0');
+        }));
+
+        $this->prepDb();
+
+        $this->assertEquals([], $this->filterDiscussions([], 5));
+    }
+
+    /**
+     * @test
+     */
+    public function filter_mutator_has_effect_if_added_with_invokable_class()
+    {
+        $this->extend((new Extend\Filter(DiscussionFilterer::class))->addFilterMutator(CustomFilterMutator::class));
+
+        $this->prepDb();
+
+        $this->assertEquals([], $this->filterDiscussions([], 5));
+    }
+}
+
+class NoResultFilter implements FilterInterface
+{
+    public function getFilterKey(): string
+    {
+        return 'noResult';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function filter(FilterState $filterState, string $filterValue, bool $negate)
+    {
+        if ($filterValue) {
+            $filterState->getQuery()
+                ->whereRaw('0=1');
+        }
+    }
+}
+
+class CustomFilterMutator
+{
+    public function __invoke($query, $actor, $filters, $sort)
+    {
+        $query->getQuery()->whereRaw('1=0');
+    }
+}
diff --git a/tests/integration/extenders/SimpleFlarumSearchTest.php b/tests/integration/extenders/SimpleFlarumSearchTest.php
index 2a874cf76..52d8dfa9a 100644
--- a/tests/integration/extenders/SimpleFlarumSearchTest.php
+++ b/tests/integration/extenders/SimpleFlarumSearchTest.php
@@ -13,9 +13,9 @@ use Carbon\Carbon;
 use Flarum\Discussion\Search\DiscussionSearcher;
 use Flarum\Extend;
 use Flarum\Search\AbstractRegexGambit;
-use Flarum\Search\AbstractSearch;
 use Flarum\Search\GambitInterface;
 use Flarum\Search\SearchCriteria;
+use Flarum\Search\SearchState;
 use Flarum\Tests\integration\RetrievesAuthorizedUsers;
 use Flarum\Tests\integration\TestCase;
 use Flarum\User\User;
@@ -64,7 +64,7 @@ class SimpleFlarumSearchTest extends TestCase
 
         $actor = User::find(1);
 
-        $criteria = new SearchCriteria($actor, $query);
+        $criteria = new SearchCriteria($actor, ['q' => $query]);
 
         return $this->app()->getContainer()->make(DiscussionSearcher::class)->search($criteria, $limit)->getResults();
     }
@@ -142,7 +142,7 @@ class NoResultFullTextGambit implements GambitInterface
     /**
      * {@inheritdoc}
      */
-    public function apply(AbstractSearch $search, $searchValue)
+    public function apply(SearchState $search, $searchValue)
     {
         $search->getQuery()
             ->whereRaw('0=1');
@@ -151,12 +151,18 @@ class NoResultFullTextGambit implements GambitInterface
 
 class NoResultFilterGambit extends AbstractRegexGambit
 {
-    protected $pattern = 'noResult:(.+)';
+    /**
+     * {@inheritdoc}
+     */
+    public function getGambitPattern()
+    {
+        return 'noResult:(.+)';
+    }
 
     /**
      * {@inheritdoc}
      */
-    public function conditions(AbstractSearch $search, array $matches, $negate)
+    public function conditions(SearchState $search, array $matches, $negate)
     {
         $noResults = trim($matches[1], ' ');
         if ($noResults == '1') {