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Welcome to the rack-vendor_accept_header gem. It provides rack middleware that parses vendor based mime types in the HTTP Accept header.

GET /something HTTP/1.1
Accept: application/vnd.acme.v3+json

The primary impetus for doing this is to be able to use vendor mime types in the HTTP Accept header for REST API versioning as well as for content negotiation. The GitHub API's usage of Media Types is an excellent example of this.


Add this line to your application's Gemfile:

gem 'rack-vendor_accept_header'

And then execute:

$ bundle

Or install it yourself as:

$ gem install rack-vendor_accept_header


Given that this is rack middleware, it can be used with pure rack applications, or with the vast number of web frameworks that are built on top of rack. This includes Ruby on Rails, Sinatra, Grape, etc. Details on using rack middleware within each of these framework can be found within their respective documentation. However, the following is a quick example of how you would register this rack middleware in Sinatra.

use Rack::VendorAcceptHeader

When you use this middleware it parses and exposes the type, sub_type, context, and version out of the vendor based mime type HTTP Accept header.

GET /something HTTP/1.1
Accept: application/vnd.acme.v3+json

Given the example above this middleware would expose these components in the rack env as follows:

request.env['vnd_type']     # => 'application'
request.env['vnd_sub_type'] # => 'json'
request.env['vnd_version']  # => '3'
request.env['vnd_context']  # => 'acme'


If you are interested in any of the references around this use case and the details around it. Please see the following.


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.