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Onebox is a library for turning media URLs into simple HTML previews of the resource.

Onebox currently has support for page, image, and video URLs for many popular sites.

It's great if you want users to input URLs and have your application convert them into rich previews for display. For example, a link to a YouTube video would be automatically converted into a video player.

It was originally created for Discourse but has since been extracted into this convenient gem for all to use!


Using onebox is fairly simple! First, make sure the library is required:

require "onebox"

Then pass a link to the library's interface:

require "onebox"

url = ""
preview = Onebox.preview(url)

This will contain a simple Onebox::Preview object that handles all the transformation. From here you either call Onebox::Preview#to_s or just pass the object to a string:

require "onebox"

url = ""
preview = Onebox.preview(url)
"#{preview}" == preview.to_s #=> true

Twitch Onebox

To be able to embed Twitch video and clips, pass hostname in the options to Onebox.preview

preview = Onebox.preview(url, hostname: '')

Ruby Support

The onebox library is supported on all "officially" supported versions of Ruby.

This means you must be on Ruby 2.4 or above for it to work.

Development Preview Interface

The onebox gem comes with a development server for previewing the results of your changes. You can run it by running bundle exec rake server after checking out the project. You can then try out URLs.

The server doesn't reload code changes automatically (PRs accepted!) so make sure to hit CTRL-C and restart the server to try a code change out.

Adding Support for a new URL

  1. Check if the site supports oEmbed or Open Graph. If it does, you can probably get away with just allowing the URL in Onebox::Engine::AllowlistedGenericOnebox (see: Allowlisted Generic Onebox caveats). If the site does not support open standards, you can create a new engine.

  2. Create new onebox engine

     # in lib/onebox/engine/name_onebox.rb
     module Onebox
       module Engine
         class NameOnebox
           include LayoutSupport
           include HTML
           def data
               url: @url,
               name: raw.css("h1").inner_text,
               image: raw.css("#main-image").first["src"],
               description: raw.css("#postBodyPS").inner_text
  3. Create new onebox spec using FakeWeb

     # in spec/lib/onebox/engine/name_spec.rb
     require "spec_helper"
     describe Onebox::Engine::NameOnebox do
       let(:link) { "" }
       let(:html) { }
       before do
         fake(link, response("name"))
       it "has the video's title" do
         expect(html).to include("title")
       it "has the video's still shot" do
         expect(html).to include("photo.jpg")
       it "has the video's description" do
         expect(html).to include("description")
       it "has the URL to the resource" do
         expect(html).to include(link)
  4. Create new mustache template

     # in templates/name.mustache
     <div class="onebox">
       <a href="{{url}}">
         <h2 class="host"></h2>
         <img src="{{image}}" />
  5. Create new fixture from HTML response for your FakeWeb request(s)

     curl --output spec/fixtures/oneboxname.response -L -X GET
  6. Require in Engine module

     # in lib/onebox/engine.rb
     require_relative "engine/name_onebox"

Allowlisted Generic Onebox caveats

The Allowlisted Generic Onebox has some caveats for its use, beyond simply allowlisting the domain.

  1. The domain must be allowlisted
  2. The URL you're oneboxing cannot be a root url (e.g. won't work, but will)
  3. If the oneboxed URL responds with oEmbed and has a rich type: the html content must contain an <iframe>. Responses without an iframe will not be oneboxed.

Ignoring Canonical URLs

Onebox prefers to use canonical URLs instead of the raw inputted URL when searching for Open Graph metadata. If your site's canonical URL does not have opengraph metadata, use the og:ignore_canonical property to have Onebox ignore the canonical URL.

<meta property="og:ignore_canonical" content="true" />


Add this line to your application's Gemfile:

gem "onebox"

And then execute:

$ bundle

Or install it yourself as:

$ gem install onebox

Issues / Discussion

Discussion of the Onebox gem, its development and features should be done on Discourse Meta.


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request