diff --git a/Gemfile b/Gemfile
index ff7471e77..bf6444978 100644
--- a/Gemfile
+++ b/Gemfile
@@ -46,6 +46,7 @@ gem 'request_store'
 gem 'builder'
 # gem 'did_you_mean' # github.com/yuki24/did_you_mean/issues/117
 gem 'term-ansicolor', require: "term/ansicolor"
+gem 'puma'
 
 # needed for looser jpeg header compat
 gem 'ruby-imagespec', :require => "image_spec", :git => "https://github.com/r888888888/ruby-imagespec.git", :branch => "exif-fixes"
@@ -88,4 +89,6 @@ group :test do
   gem "webmock"
   gem "minitest-ci"
   gem "mock_redis"
+  gem "capybara"
+  gem "selenium-webdriver"
 end
diff --git a/Gemfile.lock b/Gemfile.lock
index 588c7f180..7e552d1cc 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -121,6 +121,16 @@ GEM
       sshkit (~> 1.3)
     capistrano3-unicorn (0.2.1)
       capistrano (~> 3.1, >= 3.1.0)
+    capybara (3.29.0)
+      addressable
+      mini_mime (>= 0.1.3)
+      nokogiri (~> 1.8)
+      rack (>= 1.6.0)
+      rack-test (>= 0.6.3)
+      regexp_parser (~> 1.5)
+      xpath (~> 3.2)
+    childprocess (2.0.0)
+      rake (< 13.0)
     chronic (0.10.2)
     cityhash (0.9.0)
     coderay (1.1.2)
@@ -289,6 +299,8 @@ GEM
     pry-rails (0.3.9)
       pry (>= 0.10.4)
     public_suffix (4.0.1)
+    puma (4.1.1)
+      nio4r (~> 2.0)
     rack (2.0.7)
     rack-contrib (2.1.0)
       rack (~> 2.0)
@@ -335,6 +347,7 @@ GEM
     recaptcha (5.1.0)
       json
     redis (4.1.2)
+    regexp_parser (1.6.0)
     representable (2.3.0)
       uber (~> 0.0.7)
     request_store (1.4.1)
@@ -352,6 +365,9 @@ GEM
       crass (~> 1.0.2)
       nokogiri (>= 1.8.0)
       nokogumbo (~> 2.0)
+    selenium-webdriver (3.142.4)
+      childprocess (>= 0.5, < 3.0)
+      rubyzip (~> 1.2, >= 1.2.2)
     shoulda-context (1.2.2)
     shoulda-matchers (4.1.2)
       activesupport (>= 4.2.0)
@@ -435,6 +451,8 @@ GEM
     websocket-extensions (0.1.4)
     whenever (1.0.0)
       chronic (>= 0.6.3)
+    xpath (3.2.0)
+      nokogiri (~> 1.8)
     zeitwerk (2.1.10)
 
 PLATFORMS
@@ -455,6 +473,7 @@ DEPENDENCIES
   capistrano-rails
   capistrano-rbenv
   capistrano3-unicorn
+  capybara
   cityhash
   daemons
   delayed_job
@@ -483,6 +502,7 @@ DEPENDENCIES
   pry-byebug
   pry-inline
   pry-rails
+  puma
   rack-mini-profiler
   rails (~> 6.0)
   rake
@@ -496,6 +516,7 @@ DEPENDENCIES
   ruby-vips
   rubyzip
   sanitize
+  selenium-webdriver
   shoulda-context
   shoulda-matchers
   simple_form
diff --git a/test/application_system_test_case.rb b/test/application_system_test_case.rb
new file mode 100644
index 000000000..6faf93767
--- /dev/null
+++ b/test/application_system_test_case.rb
@@ -0,0 +1,6 @@
+require "test_helper"
+
+class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
+  include SystemTestHelper
+  driven_by :selenium, using: :firefox, screen_size: [1400, 1400]
+end
diff --git a/test/system/autocomplete_test.rb b/test/system/autocomplete_test.rb
new file mode 100644
index 000000000..4326a1176
--- /dev/null
+++ b/test/system/autocomplete_test.rb
@@ -0,0 +1,127 @@
+require "application_system_test_case"
+
+class AutocompleteTest < ApplicationSystemTestCase
+  def autocomplete(id, *keys)
+    fill_in id: id, with: ""
+    find_by_id(id).send_keys(keys)
+  end
+
+  def assert_autocomplete_equals(expected_results, text, id:)
+    autocomplete(id, text)
+
+    assert_selector 'ul.ui-autocomplete li', count: expected_results.size
+    expected_results.each do |result|
+      assert_selector "li[data-autocomplete-value='#{result}']", count: 1
+    end
+  end
+
+  def assert_search_autocomplete_equals(values, text)
+    visit posts_path unless current_path == posts_path
+    assert_autocomplete_equals(values, text, id: "tags")
+  end
+
+  def assert_metatag_autocomplete_equals(values, metatag)
+    results = values.map { |value| "#{metatag.downcase}:#{value}" }
+    assert_search_autocomplete_equals(results, "#{metatag}:")
+  end
+
+  def assert_mention_autocomplete_equals(values, text)
+    visit new_forum_post_path unless current_path == new_forum_post_path
+    assert_autocomplete_equals(values, text, id: "forum_post_body")
+  end
+
+  context "Autocomplete" do
+    context "for post searches" do
+      should "work for static metatags" do
+        assert_metatag_autocomplete_equals(%w[any none], "child")
+        assert_metatag_autocomplete_equals(%w[any none], "parent")
+        assert_metatag_autocomplete_equals(%w[rating note status], "locked")
+        assert_metatag_autocomplete_equals(%w[safe questionable explicit], "rating")
+        assert_metatag_autocomplete_equals(%w[gif jpg mp4 png swf webm zip], "filetype")
+        assert_metatag_autocomplete_equals(%w[any none disinterest poor_quality breaks_rules], "disapproval")
+        assert_metatag_autocomplete_equals(%w[active any banned deleted flagged modqueue pending unmoderated], "status")
+      end
+
+      should "work for username metatags" do
+        %w[user approver commenter comm noter noteupdater artcomm fav ordfav appealer flagger upvote downvote].each do |metatag|
+          assert_search_autocomplete_equals(["#{metatag}:DanbooruBot"], "#{metatag}:Danbo")
+          assert_search_autocomplete_equals(["#{metatag}:DanbooruBot"], "-#{metatag}:Danbo")
+        end
+      end
+
+      should "work for pool metatags" do
+        @user = create(:user)
+        as(@user) { create(:pool, name: "Cute") }
+        as(@user) { create(:post, tag_string: "pool:Cute") }
+
+        assert_search_autocomplete_equals(["pool:Cute"], "pool:c")
+        assert_search_autocomplete_equals(["pool:Cute"], "pool:cute")
+        assert_search_autocomplete_equals(["pool:Cute"], "pool:CUTE")
+        assert_search_autocomplete_equals(["pool:Cute"], "POOL:cute")
+        assert_search_autocomplete_equals(["pool:Cute"], "pool:*ute")
+        assert_search_autocomplete_equals(["pool:Cute"], "-pool:cute")
+        assert_search_autocomplete_equals(["pool:Cute"], "~pool:cute")
+
+        assert_search_autocomplete_equals(["ordpool:Cute"], "ordpool:cute")
+        assert_search_autocomplete_equals(["ordpool:Cute"], "ORDPOOL:cute")
+      end
+
+      should "work for regular tags" do
+        create(:tag, name: "bkub", post_count: 42)
+
+        assert_search_autocomplete_equals(["bkub"], "b")
+        assert_search_autocomplete_equals(["bkub"], "bkub")
+        assert_search_autocomplete_equals(["bkub"], "BKUB")
+        assert_search_autocomplete_equals(["bkub"], " bkub")
+        assert_search_autocomplete_equals(["bkub"], "one two bkub")
+
+        assert_search_autocomplete_equals(["bkub"], "-bkub")
+        assert_search_autocomplete_equals(["bkub"], "~bkub")
+        assert_search_autocomplete_equals(["bkub"], "-BKUB")
+        assert_search_autocomplete_equals(["bkub"], "~BKUB")
+
+        assert_search_autocomplete_equals(["bkub"], "art:bkub")
+        assert_search_autocomplete_equals(["bkub"], "copy:bkub")
+        assert_search_autocomplete_equals(["bkub"], "char:bkub")
+        assert_search_autocomplete_equals(["bkub"], "gen:bkub")
+        assert_search_autocomplete_equals(["bkub"], "meta:bkub")
+        assert_search_autocomplete_equals(["bkub"], "-char:bkub")
+        assert_search_autocomplete_equals(["bkub"], "~char:bkub")
+
+        assert_search_autocomplete_equals(["bkub"], "b*")
+        assert_search_autocomplete_equals(["bkub"], "B*")
+        assert_search_autocomplete_equals(["bkub"], "*b")
+        assert_search_autocomplete_equals(["bkub"], "*bkub*")
+
+        assert_search_autocomplete_equals([], " ")
+        assert_search_autocomplete_equals([], "one")
+        assert_search_autocomplete_equals([], "one two")
+      end
+
+      should "insert completions on click" do
+        visit posts_path
+
+        autocomplete("tags", "rating:s")
+        first("ul.ui-autocomplete li").click
+        assert_equal("rating:safe ", find_field(id: "tags").value)
+
+        autocomplete("tags", "one two rating:s")
+        first("ul.ui-autocomplete li").click
+        assert_equal("one two rating:safe ", find_field(id: "tags").value)
+      end
+    end
+
+    context "for username mentions" do
+      should "work" do
+        signup "member"
+
+        assert_mention_autocomplete_equals(["@member"], "@m")
+        assert_mention_autocomplete_equals(["@member"], "@member")
+        assert_mention_autocomplete_equals(["@member"], "@MEMBER")
+        assert_mention_autocomplete_equals(["@member"], "one two @member")
+
+        # assert_mention_autocomplete_equals(["@member"], "<@member")
+      end
+    end
+  end
+end
diff --git a/test/test_helpers/system_test_helper.rb b/test/test_helpers/system_test_helper.rb
new file mode 100644
index 000000000..eeefffec6
--- /dev/null
+++ b/test/test_helpers/system_test_helper.rb
@@ -0,0 +1,9 @@
+module SystemTestHelper
+  def signup(name, password: "password")
+    visit new_user_path
+    fill_in "Name", with: name
+    fill_in "Password", with: password
+    fill_in "Password confirmation", with: password
+    click_button "Sign up"
+  end
+end