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Include swagger-ui as Rails engine and document your API with simple YAML files.

Gem Version Build Status Code Climate


Swagger UI version Rails version
2.2.10 >= 4.2, <6


  • Supports API documentation versioning / multiple APIs documentation
  • Easily configurable Swagger interface and OAuth2 authorization
  • Enables using Swagger interface translations
  • Works with API-only applications
  • Simple, clear and actively maintained 🙆‍♀️


Working on a Rails API, I've wanted to document my endpoints in the clearest and easiest way possible. My goal was to have the documentation separated from the actual codebase and to have a web UI version of Swagger for testing and reading it. Using Rails 5 default API, I didn't need to include Grape, so I took a look into some other existing solutions. Most of them were no longer supported (e.g. swagger_engine and swagger-ui_rails) or required adding some extra code for the actual documentation (e.g. swagger-docs). Also, none of them supported Swagger web UI configuration, so I decided to write and maintain a gem on my own that would allow others to include Swagger web UI as Rails engine and support writing simple documentation in YAML files.


Add to Gemfile

gem 'swagger_ui_engine'

And then run:

$ bundle



Add to your config/routes.rb

mount SwaggerUiEngine::Engine, at: "/api_docs"

You can place this route under admin_constraint or other restricted path, or configure basic HTTP authentication.

Devise auth

authenticate :user, lambda { |u| u.admin? } do
  mount SwaggerUiEngine::Engine, at: "/api_docs"

Basic HTTP auth

Set admin username and password in an initializer:

# config/initializers/swagger_ui_engine.rb

SwaggerUiEngine.configure do |config|
  config.admin_username = ENV['ADMIN_USERNAME']
  config.admin_password = ENV['ADMIN_PASSWORD']


Versioned API documentations

Set the path of your json/yaml versioned documentations in an initializer:

# config/initializers/swagger_ui_engine.rb

SwaggerUiEngine.configure do |config|
  config.swagger_url = {
    v1: 'api/v1/swagger.yaml',
    v2: 'api/v2/swagger.yaml',

and place your main documentation file under /public/api path.

Single API documentation

NOTE: This is a compatibility patch for the SwaggerUiEngine gem versions <= 0.0.5. It's recommended to version your API documentation from the beginning.

You can define your main documentation url in a hash value (same way as in the versioned documentations) or pass single string with the url:

# config/initializers/swagger_ui_engine.rb

SwaggerUiEngine.configure do |config|
  config.swagger_url = 'api/swagger.yaml'


Config Name Swagger parameter name Description
config.swagger_url url The url pointing swagger.yaml (Swagger 2.0) as per OpenAPI Spec. Accepts a Hash, with API version names as keys and documentation URLs as values. Also accepts a String pointing to documentation for all versions.
config.doc_expansion docExpansion Controls how the API listing is displayed. It can be set to 'none' (default), 'list' (shows operations for each resource), or 'full' (fully expanded: shows operations and their details).
config.model_rendering defaultModelRendering Controls how models are shown when the API is first rendered. It can be set to 'model' or 'schema', and the default is 'schema'.
config.request_headers showRequestHeaders Whether or not to show the headers that were sent when making a request via the 'Try it out!' option. Defaults to false.
config.json_editor jsonEditor Enables a graphical view for editing complex bodies. Defaults to false.
config.translator_enabled translations Enables Swagger Ui translations. Defaults to false.
config.validator_enabled validatorUrl Enables documentation validator. Defaults to false (validatorUrl: 'null').

OAuth2 configuration

You can configure OAuth2 default authorization.

Config Name Swagger parameter name Description
config.oauth_client_id client_id Default clientId. MUST be a string
config.oauth_client_secret client_secret Default clientSecret. MUST be a string
config.oauth_realm realm realm query parameter (for oauth1) added to authorizationUrl and tokenUrl . MUST be a string
config.oauth_app_name appName application name, displayed in authorization popup. MUST be a string
config.oauth_scope_separator scopeSeparator scope separator for passing scopes, encoded before calling, default value is a space (encoded value %20). MUST be a string
config.oauth_query_string_params additionalQueryStringParams Additional query parameters added to authorizationUrl and tokenUrl. MUST be an object

Edit your json/yaml files

You can use Swagger editor to write and validate your Swagger docs.

Example app

Here's an example use of SwaggerUiEngine in Rails application.


You're very much welcome to contribute to this repository. Start by creating a Github issue and describing your change thoroughly. If you decide to publish a pull request, please make sure it points to the latest versioned branch instead of master.


This project is available under MIT-LICENSE. ☀️