diff --git a/ext/filter/info.php b/ext/filter/info.php
new file mode 100644
index 000000000..16a2574ab
--- /dev/null
+++ b/ext/filter/info.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shimmie2;
+
+class FilterInfo extends ExtensionInfo
+{
+    public const KEY = "filter";
+
+    public string $key = self::KEY;
+    public string $name = "Filter Tags";
+    public array $authors = ["Danbooru Project" => "", "Discomrade" => ""];
+    public string $license = "WTFPL";
+    public string $description = "Allow users to filter out tags.";
+    public ?string $documentation = "Admins can set default filters and users can override them in user settings. This is derived from Danbooru's blacklist code, it works in the user's browser with JavaScript, and will hide posts until the filter runs.";
+}
diff --git a/ext/filter/main.php b/ext/filter/main.php
new file mode 100644
index 000000000..1735b13c5
--- /dev/null
+++ b/ext/filter/main.php
@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shimmie2;
+
+class Filter extends Extension
+{
+    /** @var FilterTheme */
+    protected Themelet $theme;
+
+    public function onInitExt(InitExtEvent $event): void
+    {
+        global $config;
+        $config->set_default_string("filter_tags", "spoilers\nguro\nscat\nfurry -rating:s\n");
+    }
+
+    public function onPageRequest(PageRequestEvent $event): void
+    {
+        global $page;
+        $this->theme->addFilterBox();
+        $page->add_html_header("<script>
+        Array.from(document.getElementsByClassName('thumb')).forEach(function(post) {
+            post.style.display='none';
+        });</script>");
+    }
+
+    public function onSetupBuilding(SetupBuildingEvent $event): void
+    {
+        $sb = $event->panel->create_new_block("Filters");
+        $sb->add_longtext_option("filter_tags", 'Default filtered tags');
+        $sb->add_label("This controls the tags which are hidden by default. This feature currently requires JavaScript. Separate filters by line, or by commas. You can enter multiple tags per filter, as well as negative tags.");
+    }
+
+    public function onInitUserConfig(InitUserConfigEvent $event): void
+    {
+        global $config;
+        $event->user_config->set_default_string("filter_tags", $config->get_string("filter_tags"));
+    }
+
+    public function onUserOptionsBuilding(UserOptionsBuildingEvent $event): void
+    {
+        global $user;
+
+        $sb = $event->panel->create_new_block("Filters");
+        $sb->add_longtext_option("filter_tags", 'Default filtered tags');
+        $sb->add_label("This controls the tags which are hidden by default. This feature currently requires JavaScript. Separate filters by line, or by commas. You can enter multiple tags per filter, as well as negative tags.");
+    }
+}
diff --git a/ext/filter/script.js b/ext/filter/script.js
new file mode 100644
index 000000000..05aa2de15
--- /dev/null
+++ b/ext/filter/script.js
@@ -0,0 +1,263 @@
+// This code is a modified, jquery-less adaptation of danbooru/app/javascript/src/javascripts/blacklists.js, with snippets from utility.js
+// The following copyright notice is a legal requirement of Danbooru's BSD 2-Clause license
+
+// Copyright (c) 2013~2021, Danbooru Project
+// All rights reserved.
+
+let Utility = {};
+
+Utility.is_subset = function(array, subarray) {
+  var all = true;
+
+  $.each(subarray, function(i, val) {
+    if ($.inArray(val, array) === -1) {
+      all = false;
+    }
+  });
+
+  return all;
+}
+
+Utility.intersect = function(a, b) {
+  a = a.slice(0).sort();
+  b = b.slice(0).sort();
+  var result = [];
+  while (a.length > 0 && b.length > 0) {
+    if (a[0] < b[0]) {
+      a.shift();
+    } else if (a[0] > b[0]) {
+      b.shift();
+    } else {
+      result.push(a.shift());
+      b.shift();
+    }
+  }
+  return result;
+}
+
+let Filter = {};
+
+Filter.entries = [];
+
+Filter.parse_entry = function(string) {
+  var entry = {
+    "tags": string,
+    "require": [],
+    "exclude": [],
+    "optional": [],
+    "disabled": false,
+    "hits": 0,
+    "min_score": null
+  };
+
+  let tags = string.split(/ +/);
+  tags.forEach(function(tag) {
+    if (tag.charAt(0) === '-') {
+      entry.exclude.push(tag.slice(1));
+    } else if (tag.charAt(0) === '~') {
+      entry.optional.push(tag.slice(1));
+    } else if (tag.match(/^score:<.+/)) {
+      var score = tag.match(/^score:<(.+)/)[1];
+      entry.min_score = parseInt(score);
+    } else {
+      entry.require.push(tag);
+    }
+  });
+  return entry;
+}
+
+Filter.parse_entries = function() {
+  var entries = document.getElementById("filter-tags").getAttribute("tags").replace(/(rating:\w)\w+/ig, "$1").toLowerCase().split(/[,\n]/);
+  entries = entries.filter(e => e.trim() !== "");
+
+  entries.forEach(function(tags) {
+    var entry = Filter.parse_entry(tags);
+    Filter.entries.push(entry);
+  });
+}
+
+Filter.toggle_entry = function(e) {
+  var link = e.target;
+  var tags = link.innerText;
+  var match = Filter.entries.find(function(entry, i) {
+    return entry.tags === tags;
+  });
+  if (match) {
+    match.disabled = !match.disabled;
+    if (match.disabled) {
+      link.classList.add("filter-inactive");
+    } else {
+      link.classList.remove("filter-inactive");
+    }
+  }
+  Filter.apply();
+  e.preventDefault();
+}
+
+Filter.update_sidebar = function() {
+  Filter.entries.forEach(function(entry) {
+    if (entry.hits.length === 0) {
+      return;
+    }
+
+    var item = document.createElement("li");
+    var link = document.createElement("a");
+    var count = document.createElement("span");
+
+    link.innerText = entry.tags;
+    link.classList.add("filter");
+    link.setAttribute("href", `/posts?tags=${encodeURIComponent(entry.tags)}`);
+    link.setAttribute("title", entry.tags);
+    link.addEventListener("click", Filter.toggle_entry);
+    let unique_hits = new Set(entry.hits).size;
+    count.innerText = unique_hits;
+    count.classList.add("tag_count");
+    item.append(link);
+    item.append(" ");
+    item.append(count);
+
+    document.getElementById("filter-list").append(item);
+  });
+
+  document.getElementById("Filtersleft").style.display = "";
+}
+
+Filter.disable_all = function() {
+  Filter.entries.forEach(function(entry) {
+    entry.disabled = true;
+  });
+  // There is no need to process the filter when disabling
+  Array.from(Filter.posts()).forEach(function(post) {
+    post.classList.remove("filtered-active");
+  });
+  document.getElementById("disable-all-filters").style.display = "none";
+  document.getElementById("re-enable-all-filters").style.display = "";
+  Array.from(document.getElementsByClassName("filter")).forEach(function(post) {
+    post.classList.add("filter-inactive");
+  });
+}
+
+Filter.enable_all = function() {
+  Filter.entries.forEach(function(entry) {
+    entry.disabled = false;
+  });
+  Filter.apply();
+  document.getElementById("disable-all-filters").style.display = "";
+  document.getElementById("re-enable-all-filters").style.display = "none";
+  Array.from(document.getElementsByClassName("filter")).forEach(function(post) {
+    post.classList.remove("filter-inactive");
+  });
+}
+
+Filter.initialize_disable_all_filters = function() {
+  if (shm_cookie_get("ui-disable-filters") === "1") {
+    Filter.disable_all();
+  } else {
+    // The filter has already been processed by this point
+    document.getElementById("disable-all-filters").style.display = "";
+  }
+
+  document.getElementById("disable-all-filters").addEventListener("click", function(e) {
+    shm_cookie_set("ui-disable-filters", "1");
+    Filter.disable_all();
+    e.preventDefault();
+  });
+
+  document.getElementById("re-enable-all-filters").addEventListener("click", function(e) {
+    shm_cookie_set("ui-disable-filters", "0");
+    Filter.enable_all();
+    e.preventDefault();
+  });
+}
+
+
+Filter.apply = function() {
+  Filter.entries.forEach(function(entry) {
+    entry.hits = [];
+  });
+
+  var count = 0
+  Array.from(Filter.posts()).forEach(function(post) {
+    count += Filter.apply_post(post);
+  });
+
+  return count;
+}
+
+Filter.apply_post = function(post) {
+  var post_count = 0;
+  Filter.entries.forEach(function(entry) {
+    if (Filter.post_match(post, entry)) {
+      let post_id = post.getAttribute("data-post-id");
+      entry.hits.push(post_id);
+      post_count += 1;
+    }
+  });
+  if (post_count > 0) {
+    Filter.post_hide(post);
+  } else {
+    Filter.post_unhide(post);
+  }
+  return post_count;
+};
+
+Filter.posts = function() {
+  return document.getElementsByClassName("thumb");
+}
+
+Filter.post_match = function(post, entry) {
+  if (entry.disabled) {
+    return false;
+  }
+
+  var score = parseInt(post.getAttribute("data-score"));
+  var score_test = entry.min_score === null || score < entry.min_score;
+
+  var tags = post.getAttribute("data-tags").split(/ +/);
+//  tags.push(...(post.getAttribute("data-pools")).split(/ +/));
+  tags.push("rating:" + post.getAttribute("data-rating"));
+//  tags.push("uploaderid:" + post.getAttribute("data-uploader-id"));
+//  post.getAttribute("flags").split(/ +/).forEach(function(v) {
+//    tags.push("status:" + v);
+//  });
+
+  return (Utility.is_subset(tags, entry.require) && score_test)
+    && (!entry.optional.length || Utility.intersect(tags, entry.optional).length)
+    && !Utility.intersect(tags, entry.exclude).length;
+}
+
+Filter.post_hide = function(post) {
+  post.classList.add("filtered");
+  post.classList.add("filtered-active");  
+
+  var video = post.querySelector("video");
+  if (video) {
+    video.pause();
+    video.currentTime = 0;
+  }
+}
+
+Filter.post_unhide = function(post) {
+  post.classList.add("filtered")
+  post.classList.remove("filtered-active");
+
+  var video = post.querySelector("video");
+  if (video) {
+    video.play();
+  }
+}
+
+Filter.initialize_all = function() {
+  Filter.parse_entries();
+
+  if (Filter.apply() > 0) {
+    Filter.update_sidebar();
+    Filter.initialize_disable_all_filters();
+  } else {
+    document.getElementById("Filtersleft").style.display = "none";
+  }
+}
+
+if (document.getElementById("Filtersleft")) {
+  Filter.initialize_all();
+}
diff --git a/ext/filter/style.css b/ext/filter/style.css
new file mode 100644
index 000000000..ead4ca372
--- /dev/null
+++ b/ext/filter/style.css
@@ -0,0 +1,4 @@
+#filter-list{padding:revert; text-align:left;}
+.thumb.filtered{display:unset}
+.thumb.filtered.filtered-active{display:none;}
+.filter-inactive,.filter-inactive:hover{text-decoration: line-through;}
\ No newline at end of file
diff --git a/ext/filter/theme.php b/ext/filter/theme.php
new file mode 100644
index 000000000..53206d14c
--- /dev/null
+++ b/ext/filter/theme.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shimmie2;
+
+class FilterTheme extends Themelet
+{
+    public function addFilterBox(): void
+    {
+        global $config, $page, $user, $user_config;
+
+        // If user is not able to set their own filters, use the default filters.
+        if ($user->can(Permissions::CHANGE_USER_SETTING)) {
+            $tags = $user_config->get_string("filter_tags");
+        } else {
+            $tags = $config->get_string("filter_tags");
+        }
+        $html = "<noscript>Post filtering requires JavaScript</noscript>
+        <ul id='filter-list' class='list-bulleted'></ul>
+        <a id='disable-all-filters' style='display: none;' href='#'>Disable all</a>
+        <a id='re-enable-all-filters' style='display: none;' href='#'>Re-enable all</a>
+        ";
+        $page->add_html_header("<meta id='filter-tags' tags='$tags'>");
+        $page->add_block(new Block("Filters", $html, "left", 10));
+    }
+}