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The best Rails 6.0+ forums engine ever. Its goal is to be as simple and feature rich as possible. Thredded works with SQLite, MySQL (v5.6.4+), and PostgreSQL. See the demo at
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Thredded is a Rails 6.0+ forum/messageboard engine. Its goal is to be as simple and feature rich as possible.

Some of the features currently in Thredded:

  • Markdown (default) and / or BBCode post formatting, with onebox and <spoiler> / [spoiler] tag support.
  • (Un)read posts tracking.
  • Email notifications, topic subscriptions, @-mentions, per-messageboard notification settings.
  • Private group messaging.
  • Full-text search using the database.
  • Pinned and locked topics.
  • List of currently online users, for all forums and per-messageboard.
  • Flexible permissions system.
  • Basic moderation.
  • Lightweight default theme configurable via Sass.
Messageboards (Thredded v0.8.2) Topics (Thredded v0.8.2)
Topic on iPhone 6 (Thredded v0.8.2) Messageboard Preferences on iPhone 6 (Thredded v0.8.2)

Thredded works with SQLite, MySQL (v5.6.4+), and PostgreSQL. Thredded has no infrastructure dependencies other than the database and, if configured in the parent application, the ActiveJob backend dependency such as Redis. Currently only MRI Ruby 2.2+ is supported. We would love to support JRuby and Rubinius as well.

If you're looking for variations on a theme - see Discourse. However, It is a full rails application and not an engine like Thredded.

Table of Contents

  • Installation
    • Creating a new Rails app with Thredded
    • Adding Thredded to an existing Rails app
    • Upgrading an existing install
    • Migrating from Forem
  • Rails compatibility
  • Views and other assets
    • Standalone layout
    • Application layout
      • Reference your paths so that Thredded can find them
      • Add Thredded styles
      • Add Thredded JavaScripts (Sprockets)
      • Add Thredded JavaScripts (Webpack)
    • User profile page
    • Customizing views
      • View hooks
    • Theming
      • Styles
  • Email and other notifications
    • Enabling auto-follow
  • I18n
  • Permissions
    • Permission methods
      • Reading messageboards
      • Posting to messageboards
      • Messaging other users (posting to private topics)
      • Moderating messageboards
      • Admin permissions
    • Default permissions
    • Handling "Permission denied" and "Not found" errors
  • Moderation
    • Disabling moderation
  • Plugins
  • Development
    • Testing
    • Ruby
    • JavaScript
    • Testing with all the databases and Rails versions locally.
    • Developing and Testing with Docker Compose


Creating a new Rails app with Thredded

Thredded provides an app generator that will generate a Rails app with Thredded, Devise, SimpleForm, RSpec, PostgreSQL, and a basic theme and navigation that is configured to work out of the box.

gem install thredded_create_app
thredded_create_app path/to/myapp

See thredded_create_app --help and the thredded_create_app repo to learn about the various options.

Then, see the rest of this Readme for more information about using and customizing Thredded.

Adding Thredded to an existing Rails app

Add the gem to your Gemfile:

gem 'thredded', '~> 1.1'

Add the Thredded initializer to your parent app by running the install generator.

rails generate thredded:install

Thredded needs to know the base application User model name and certain columns on it. Configure these in the initializer installed with the command above.

Then, copy the migrations over to your parent application and migrate:

rake thredded:install:migrations db:migrate db:test:prepare

Mount the thredded engine in your routes file:

mount Thredded::Engine => '/forum'

You also may want to add an index to the user name column in your users table. Thredded uses it to find @-mentions and perform name prefix autocompletion on the private topic form. Add the index in a migration like so:

    connection, Thredded.user_class.table_name, Thredded.user_name_column, unique: true)

Upgrading an existing install

  1. To upgrade the initializer:
rails g thredded:install

But then compare this with the previous version to decide what to keep.

  1. To upgrade the database (in this example from v0.11 to v0.12):
# Note that for guaranteed best results you will want to run this with the thredded gem at v0.12
cp "$(bundle show thredded)"/db/upgrade_migrations/20170420163138_upgrade_thredded_v0_11_to_v0_12.rb db/migrate
rake db:migrate

Migrating from Forem

Are you currently using Forem? Thredded provides a migration to copy all of your existing data from Forem over to Thredded.

Rails compatibility

Rails Latest Thredded
Rails 6.0+ Thredded 1.1+
Rails 5.2 Thredded 1.0.1
Rails 4.2 Thredded 0.16.16

Views and other assets

Standalone layout

By default, thredded renders in its own (standalone) layout.

When using the standalone thredded layout, the log in / sign out links will be rendered in the navigation. For these links (and only for these links), Thredded makes the assumption that you are using devise as your auth library. If you are using something different you need to override the partial at app/views/thredded/shared/nav/_standalone.html.erb and use the appropriate log in / sign out path URL helpers.

You can override the partial by copying it into your app:

mkdir -p app/views/thredded/shared/nav && cp "$(bundle show thredded)/$_/_standalone.html.erb" "$_"

Application layout

You can also use Thredded with your application (or other) layout by setting Thredded.layout in the initializer.

In this case, you will need to reference your paths/routes carefully and pull in thredded assets (styles and javascript):

Reference your paths so that Thredded can find them

In your layout you will probably have links to other paths in your app (e.g. navigation links). For any url helpers (like users_path or projects_path or whatever) will need to have main_app. prefixed to them so that they can be found from thredded (main_app.users_path will work from both thredded and your app).

Add Thredded styles

In this case, you will also need to include Thredded styles and JavaScript into the application styles and JavaScript.

Add thredded styles to your application.scss:

@import "thredded";

Thredded wraps the views in a container element that has a max-width and paddings by default. If your app layout already has a container element that handles these, you can remove the max-width and paddings from the Thredded one by adding this Sass snippet after @import "thredded";:

.thredded--main-container {
  // The padding and max-width are handled by the app's container.
  max-width: none;
  padding: 0;
  @include thredded-media-tablet-and-up {
    padding: 0;

See below for customizing the styles via Sass variables.

Add Thredded JavaScripts (Sprockets)

Include thredded JavaScripts in your application.js:

//= require thredded

Thredded is fully compatible with deferred and async script loading.

Add Thredded JavaScripts (Webpack)

You can also include Thredded JavaScript into your webpack pack.

First, run bundle exec rails webpacker:install:erb.

Then, add an app/javascript/thredded_imports.js.erb file with the following contents:

<%= Thredded::WebpackAssets.javascripts %>

Finally, add the following to your app/javascript/packs/application.js:


Note that you must use require (not import) because Thredded JavaScript must be run after UJS/Turbolink start() has been called. This is because Webpack places import calls before the code in the same file (unlike require, which are placed in the same order as in the source).

Alternative JavaScript dependencies
Rails UJS version

By default, thredded loads rails-ujs. If you're using Rails before v5.1, you need to add rails-ujs to your Gemfile.

If you'd like it to use jquery_ujs instead, run this command from your app directory:

mkdir -p app/assets/javascripts/thredded/dependencies/
printf '//= require jquery3\n//= require jquery_ujs\n' > app/assets/javascripts/thredded/dependencies/ujs.js
Timeago version

By default, thredded loads timeago.js.

If you'd like to use jquery.timeago or rails-timeago instead, run this command from your app directory:

mkdir -p app/assets/javascripts/thredded/dependencies/
echo '//= require jquery.timeago' > app/assets/javascripts/thredded/dependencies/timeago.js

You will also need to adjust the //= require statements for timeago locales if your site is translated into multiple languages. For jquery.timeago, these need to be require after thredded/dependencies but before thredded/thredded. E.g. for Brazilian Portuguese with jquery.timeago:

//= require thredded/dependencies
//= require locales/
//= require thredded/thredded

Thredded page title and ID

Thredded views also provide two content_tags available to yield - :thredded_page_title and :thredded_page_id. The views within Thredded pass those up through to your layout if you would like to use them.

User profile page

Thredded does not provide a user's profile page, but it provides a partial for rendering the user's recent posts in your app's user profile page. Here is how you can render it in your app:

<%= Thredded::ApplicationController.render partial: 'thredded/users/posts', locals: {
      posts: Thredded.posts_page_view(scope: user.thredded_posts.order_newest_first.limit(5),
                                      current_user: current_user) } %>

The user above is the user whose posts are rendered, and current_user is the user viewing the posts or nil. The policy scopes that limit the posts to the ones current_user can see are applied automatically.

The code above uses the ApplicationController.render method introduced in Rails 5. If you're using Rails 4, you will need to add the backport_new_renderer gem to use it.

Customizing views

You can also override any views and assets by placing them in the same path in your application as they are in the gem. This uses the standard Rails mechanism for overriding engine views. For example, to copy the post view for customization:

# Copy the post view into the application to customize it:
mkdir -p app/views/thredded/posts && cp "$(bundle show thredded)/$_/_post.html.erb" "$_"

NB: Overriding the views like this means that on every update of the thredded gem you have to check that your customizations are still compatible with the new version of thredded. This is difficult and error-prone. Whenever possible, use the styles and i18n to customize Thredded to your needs.

View hooks

Thredded provides view hooks to customize the UI before/after/replacing individual components.

View hooks allow you to render anything in the thredded view context. For example, to render a partial after the post content textarea, add the snippet below to the config/initializers/thredded.rb initializer:

Rails.application.config.to_prepare do
  Thredded.view_hooks.post_form.content_text_area.config.before do |form:, **args|
    # This is render in the Thredded view context, so all Thredded helpers and URLs are accessible here directly.
    render 'my/partial', form: form

You can use the post content textarea hook to add things like wysiwyg/wymean editors, buttons, help links, help copy, further customization for the textarea, etc.

To see the complete list of view hooks and their arguments, run:

grep view_hooks -R --include '*.html.erb' "$(bundle show thredded)"


The engine comes by default with a light and effective implementation of the views, styles, and javascript. Once you mount the engine you will be presented with a "themed" version of thredded.


Thredded comes with a light Sass theme controlled by a handful of variables that can be found here:

To override the styles, override the variables before importing Thredded styles, e.g.:

// application.scss
$thredded-brand: #9c27b0;
@import "thredded";

If you are writing a Thredded plugin, import the thredded/base Sass package instead. The base package only defines variables, mixins, and %-placeholders, so it can be imported safely without producing any duplicate CSS.

Email and other notifications

Thredded sends several notification emails to the users. You can override in the same way as the views. See this page on how to style the emails.

If you use Rails Email Preview, you can include Thredded emails into the list of previews by adding Thredded::BaseMailerPreview.preview_classes to the Rails Email Preview preview_classes config option.

You can also turn off the email notifier totally, or add other notifiers (e.g. Pushover, possibly Slack) by adjusting the Thredded.notifiers configuration in your initializer. See the default initializer for examples.

You must configure the address the email appears to be from (Thredded.email_from). This address is also used as the "To" address for both email notifcations, as all the recipients are on bcc.

Enabling auto-follow

In some cases, you'll want all users to auto-follow new messageboard topics by default. This might be useful for a team messageboard or a company announcements board, for example. To enable user auto-follow of new topics, run the following migration(s):

change_column_default :thredded_user_preferences, :auto_follow_topics, true


Thredded is mostly internationalized. It is currently available in English, Brazilian Portuguese, Chinese (Simplified), German, Polish, Italian, Russian, French, and Spanish. We welcome PRs adding support for new languages.

Here are the steps to ensure the best support for your language if it isn't English:

  1. Add rails-i18n and kaminari-i18n to your Gemfile.

  2. Require the translations for timeago.js in your JavaScript. E.g. if you want to add German and Brazilian Portuguese:


    //= require thredded/dependencies/timeago
    //= require timeago/locales/de
    //= require timeago/locales/pt_BR
    //= require thredded


    <% timeago_root = File.join(Gem.loaded_specs['timeago_js'].full_gem_path, 'assets', 'javascripts') %>
    import "<%= File.join(timeago_root, 'timeago.js') %>";
    <%= %w[de pt_BR].map { |locale| %(import "#{File.join(timeago_root, "timeago/locales/#{locale}.js")}";) } * "\n" %>
    <%= Thredded::WebpackAssets.javascripts %>

    Note that it is important that timeago and its locales are required before Thredded.

  3. To generate URL slugs for messageboards, categories, and topics with support for more language than English, you can use a gem like babosa. Add babosa to your Gemfile and uncomment the Thredded.slugifier proc for babosa in the initializer.


Thredded comes with a flexible permissions system that can be configured per messageboard/user. It calls a handful of methods on the application User model to determine permissions for logged in users, and calls the same methods on Thredded:NullUser to determine permissions for non-logged in users.

Permission methods

The methods used by Thredded for determining the permissions are described below.

  • To customize permissions for logged in users, override any of the methods below on your User model.
  • To customize permissions for non-logged in users, override these methods on Thredded::NullUser.

Reading messageboards

  1. A list of messageboards that a given user can read:
# @return [ActiveRecord::Relation] messageboards that the user can read
  1. A list of users that can read a given list of messageboards:
# @param messageboards [Array<Thredded::Messageboard>]
# @return [ActiveRecord::Relation] users that can read the given messageboards

Posting to messageboards

A list of messageboards that a given user can post in.

# @return [ActiveRecord::Relation<Thredded::Messageboard>] messageboards that the user can post in

Messaging other users (posting to private topics)

A list of users a given user can message:

# @return [ActiveRecord::Relation] the users this user can include in a private topic

Moderating messageboards

A list of messageboards that a given user can moderate:

# @return [ActiveRecord::Relation<Thredded::Messageboard>] messageboards that the user can moderate

Admin permissions

Includes all of the above for all messageboards:

# @return [boolean] Whether this user has full admin rights on Thredded

Default permissions

Below is an overview of the default permissions, with links to the implementations:

Read Post Message Moderate Administrate
Logged in ✅ All ✅ All Readers of the messageboards
the user can post in
moderator_column admin_column
Not logged in ❌ No ❌ No ❌ No ❌ No

Handling "Permission denied" and "Not found" errors

Thredded defines a number of Exception classes for not found / permission denied errors. The complete list can be found here.

Currently, the default behaviour is to render an error message with an appropriate response code within the Thredded layout. You may want to override the handling for Thredded::Errors::LoginRequired to render a login form instead. For an example of how to do this, see the initializer.


Thredded comes with two options for the moderation system:

  1. Reactive moderation, where posts from first-time users are published immediately but enter the moderation queue (default).
  2. Pre-emptive moderation, where posts from first-time users are not published until they have been approved.

This is controlled by the Thredded.content_visible_while_pending_moderation setting.

Users, topics, and posts can be in one of three moderation states: pending_moderation, approved, and blocked. By default, new users are pending_moderation, and new posts and topics inherit their default moderation_state from the user's.

When you approve a new user's post, all of their later posts will be approved automatically.

Additionally, users always see their own posts regardless of the moderation state. For blocked users, this means they might not realize they have been blocked right away.

Blocked users cannot send private messages.

Disabling moderation

To disable moderation, e.g. if you run internal forums that do not need moderation, run the following migration:

change_column_default :thredded_user_details, :moderation_state, 1 # approved

Requiring authentication to access Thredded

To require users to be authenticated to access any part of Thredded, add the following to your initializer:

# config/initializers/thredded.rb
Rails.application.config.to_prepare do
  Thredded::ApplicationController.module_eval do
    # Require authentication to access the forums:
    before_action :thredded_require_login!

    # You may also want to render a login form after the
    # "Please sign in first" message:
    rescue_from Thredded::Errors::LoginRequired do |exception|
      # Place the code for rendering the login form here, for example:[:notice] = exception.message
      controller =
      controller.request = request
      controller.request.env['devise.mapping'] = Devise.mappings[:user]
      controller.response = response
      controller.response_options = { status: :forbidden }


The following official plugins are available for Thredded:

Thredded is built for extensibility, and writing plugins for it is easy. If you plan on extending Thredded functionality in a way others may benefit from, please consider making it a plugin.


To be more clear - this is the for when you are working on this gem. Not for when you are implementing it into your Rails app.

First, to get started, migrate and seed the database (SQLite by default):

# Create, migrate, and seed the development database with fake forum users, topics, and posts:
bin/rails db:create db:migrate db:seed

Install NPM dependencies for the dummy app:

cd spec/dummy && yarn && cd -

Then, start the dummy app server:

bin/rails s

By default, the dummy app server uses Webpack for JavaScript. To use Sprockets instead, run:


alternatively you can use guard (which comes with activereload to make development more pleasant) with:

bundle exec guard


In order to run the tests locally, you will need to be running webpack-dev-server (or do a manual compilation):

cd spec/dummy && yarn && cd -
BUNDLE_GEMFILE="${PWD}/Gemfile" spec/dummy/bin/webpack-dev-server

Then to run the tests, just run rspec. The test suite will re-create the test database on every run, so there is no need to run tasks that maintain the test database.

By default, SQLite is used in development and test. On Travis, the tests will run using SQLite, PostgreSQL, MySQL, and all the supported Rails versions.

The test suite requires Chromium v59+ and its WebDriver installed:

On Ubuntu, run:

sudo apt-get install chromium-chromedriver

On Mac, run:

brew install --cask chromium
brew install --cask chromedriver

To get better page saves (page.save_and_open_page) from local capybara specs ensure you are running the server locally and set export CAPYBARA_ASSET_HOST=http://localhost:3000 (or whatever host/port your server is on) before running your test suite.


Thredded Ruby code formatting is ensured by Rubocop. Run rubocop -a to ensure a consistent code style across the codebase.

Thredded is documented with YARD and you can use the inch gem or the Inch CI to find code that lacks documentation.


Currently, Thredded JavaScript is written in the subset of ES6 that does not require Babel polyfills. We're waiting for the ES6/7 support on Rails to improve before updating this to full Babel.

All Thredded JavaScript is compatible with the following Turbolinks options:

  • No Turbolinks.
  • Turbolinks 5.
  • Turbolinks Classic.
  • Turbolinks Classic + jquery-turbolinks.

Thredded JavaScript is also compatible with being loaded from script elements with [async] and/or [defer] attributes.

To achieve the above, all the Thredded code must register onload via Thredded.onPageLoad, e.g.:

window.Thredded.onPageLoad(() => {
  // Initialize widgets

Additionally, all the thredded views must be wrapped in a <%= thredded_page do %> block.

On Turbolinks 5 onPageLoad will run on the same DOM when the page is restored from history (because Turbolinks 5 caches a clone of the body node, so the events are lost).

This means that all DOM modifications on window.Thredded.onPageLoad must be idempotent, or they must be reverted on the turbolinks:before-cache event, e.g.:

document.addEventListener('turbolinks:before-cache', () => {
  // Destroy widgets

Testing with all the databases and Rails versions locally.

You can also test the gem with all the supported databases and Rails versions locally.

First install PostgreSQL and MySQL, and run:


Then, to test with all the databases and the default Rails version (as defined in Gemfile), run:

rake test_all_dbs

To test with a specific database and all the Rails versions, run:

# Test with SQLite3:
rake test_all_gemfiles
# Test with MySQL:
DB=mysql2 rake test_all_gemfiles
# Test with PostgreSQL:
DB=postgresql rake test_all_gemfiles

To test all combinations of supported databases and Rails versions, run:

rake test_all

Developing and Testing with Docker Compose

To quickly try out Thredded with the included dummy app, clone the source and start the included docker-compose.yml file with:

docker-compose build
docker-compose up

The above will build and run everything, daemonized, resulting in a running instance on port 9292. Running docker-compose logs will let you know when everything is up and running. Editing the source on your host machine will be reflected in the running docker'ized application.

Note that when using boot2docker on a Mac make sure you visit the boot2docker host ip at http://$(boot2docker ip):9292.

After booting up the containers you can run the test suite with the following:

docker-compose run web bundle exec rake

The docker container uses PostgreSQL.