ZRO: OpenApi 3 JSON-Doc Generator for Rails

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Concise DSL for generating OpenAPI Specification 3 (OAS3, formerly Swagger3) JSON documentation for Rails application.

  class Api::ExamplesController < ApiController
    api :update, 'POST update some thing' do
      path  :id, Integer
      query :token, String, desc: 'api token', length: 16
      form data: { phone: String }


Hi, here is ZhanDao = ▽ =
It may be a very useful tool if you want to write API document clearly.
I'm looking forward to your issue and PR!

Need Help

If you have any questions, please read the test code first.
such as api DSL and schema Obj.

Table of Contents

About OAS

Everything about OAS3 is on OpenAPI Specification

You can getting started from swagger.io

I suggest you should understand the basic structure of OAS3 at least. such as component (can help you reuse DSL code, when your apis are used with the same data structure).


Add this line to your Rails's Gemfile:

  gem 'zero-rails_openapi'
  # or
  gem 'zero-rails_openapi', github: 'zhandao/zero-rails_openapi'

And then execute:

  $ bundle

Or install it yourself as:

  $ gem install zero-rails_openapi


Create an initializer, configure ZRO and define your OpenApi documents.

This is the simplest example:

  # config/initializers/open_api.rb
  require 'open_api'

  OpenApi::Config.tap do |c|
    # [REQUIRED] The output location where .json doc file will be written to.
    c.file_output_path = 'public/open_api'

    c.open_api_docs = {
        # The definition of the document `homepage`.
        homepage: {
            # [REQUIRED] ZRO will scan all the descendants of base_doc_classes, then generate their docs.
            base_doc_classes: [Api::V1::BaseController],

            # [REQUIRED] OAS Info Object: The section contains API information.
            info: {
                # [REQUIRED] The title of the application.
                title: 'Homepage APIs',
                # Description of the application.
                description: 'API documentation of Rails Application. <br/>' \
                             'Optional multiline or single-line Markdown-formatted description ' \
                             'in [CommonMark](http://spec.commonmark.org/) or `HTML`.',
                # [REQUIRED] The version of the OpenAPI document
                # (which is distinct from the OAS version or the API implementation version).
                version: '1.0.0'

In addition to directly using Hash, you can also use DSL to define the document information:

  # config/initializers/open_api.rb
  require 'open_api'

  OpenApi::Config.tap do |c|
    c.file_output_path = 'public/open_api'

    c.instance_eval do
      open_api :homepage_api, base_doc_classes: [ApiDoc]
      info version: '1.0.0', title: 'Homepage APIs'

For more detailed configuration: open_api.rb
See all the settings options: config.rb
See all the Document Definition DSL: config_dsl.rb

Usage - DSL

First of all, include OpenApi::DSL to your base class (which is for writing docs), for example:

  # app/controllers/api/api_controller.rb
  class ApiController < ActionController::API
    include OpenApi::DSL

DSL Usage Example

Here is the simplest usage:

  class Api::ExamplesController < ApiController
    api :index, 'GET list' do
      query :page, Integer#, desc: 'page, greater than 1', range: { ge: 1 }, dft: 1
      query :rows, Integer#, desc: 'per page', range: { ge: 1 }, default: 10

For more example, see goods_doc.rb, and examples_controller.rb, or HERE.

Basic DSL (source code)

(1) route_base [optional if you're writing DSL in controller]

  # method signature
  # usage
  route_base 'api/v1/examples'

It is optional because route_base defaults to controller_path.

Here's a trick: Using route_base, you can write the DSL somewhere else to simplify the current controller.

(2) doc_tag [optional]

  # method signature
  doc_tag(name: nil, desc: '', external_doc_url: nil)
  # usage
  doc_tag name: 'ExampleTagName', desc: "ExamplesController's APIs"

This method allows you to set the Tag (which is a node of OpenApi Object).

Tag's name defaults to controller_name. desc and external_doc_url are optional.

(3) components [optional]

  # method signature
  # usage
  components do
    # DSL for defining components
    schema :DogSchema => [ { id: Integer, name: String }, dft: { id: 1, name: 'pet' } ]
    query! :UidQuery  => [ :uid, String, desc: 'uid' ]
    resp   :BadRqResp => [ 'bad request', :json ]

  # to use component
  api :action, 'summary' do
    query :doge, :DogSchema # to use a Schema component
    param_ref :UidQuery     # to use a Parameter component
    response_ref :BadRqResp # to use a Response component

Component can be used to simplify your DSL code (that is, to refer to the defined Component object by *_ref methods).

Each RefObj is associated with components through component key. We suggest that component keys should be camelized, and must be Symbol.

(4) api_dry [optional]

This method is for DRYing.

  # method signature
  api_dry(action = :all, desc = '', &block)
  # usage
  api_dry :all, 'common response' # block ...
  api_dry :index # block ...
  api_dry [:index, :show] do
    query! #...

As you think, the block will be executed to each specified API(action) firstly.

(5) api [required]

Define the specified API (or we could say controller action).

  # method signature
  api(action, summary = '', http: nil, skip: [ ], use: [ ], &block)
  # usage
  api :index, '(SUMMARY) this api blah blah ...', # block ...

use and skip options: to use or skip the parameters defined in api_dry.

  api :show, 'summary', use: [:id] # it will only take :id from DRYed result to define the API :show

DSL methods inside api and api_dry's block

source code

These following methods in the block describe the specified API action: description, valid?, parameters, request body, responses, securities, servers.

(Here corresponds to OAS Operation Object)

(1) this_api_is_invalid!, its aliases:

  # method signature
  this_api_is_invalid!(explain = '')
  # usage
  this_api_is_invalid! 'this api is expired!'

Then deprecated of this API will be set to true.

(2) desc: description for the current API and its inputs (parameters and request body)

  # method signature
  desc(desc, param_descs = { })
  # usage
  desc "current API's description",
       id:    'desc of the parameter :id',
       email: 'desc of the parameter :email'

You can of course describe the input in it's DSL method (like query! :done ..., this line), but that will make it long and ugly. We recommend that unite descriptions in this place.

In addition, when you want to dry the same parameters (each with a different description), it will be of great use.

(3) param family methods (OAS - Parameter Object)

Define the parameters for the API (action).

  param_ref                          # for reuse component,
                                     #   it links sepcified RefObjs (by component keys) to current parameters.
  header,  path,  query,  cookie     # will pass specified parameter location to `param`
  header!, path!, query!, cookie!    # bang method of above methods
  do_* by: { parameter_definations } # batch definition parameters, such as do_path, do_query
  order                              # order parameters by names array you passed
  examples                           # define examples of parameters

The bang method (which's name is end of a exclamation point !) means this param is required, so without ! means optional.

  # `param_type` just is the location of parameter, like: query, path
  # `schema_type` is the type of parameter, like: String, Integer (must be a constant)
  # For more explanation, please click the link below ↓↓↓
  # method signature
  param(param_type, param_name, schema_type, is_required, schema_info = { })
  # usage
  param :query, :page, Integer, :req,  range: { gt: 0, le: 5 }, desc: 'page'

  # method signature
  param_ref(component_key, *component_keys) # should pass at least 1 key
  # usage
  param_ref :IdPath
  param_ref :IdPath, :NameQuery, :TokenHeader

  ### method signature
   header(param_name, schema_type = nil, **schema_info)
  header!(param_name, schema_type = nil, **schema_info)
   query!(param_name, schema_type = nil, **schema_info)
  # ...
  ### usage
  header! 'Token', String
  query!  :readed, Boolean, must_be: true, default: false
  # The same effect as above, but not simple
  param :query, :readed, Boolean, :req, must_be: true, default: false
  # When schema_type is a Object
  #   (describe by hash, key means prop's name, value means prop's schema_type)
  query :good, { name: String, price: Float, spec: { size: String, weight: Integer } }, desc: 'good info'
  # Or you can use `type:` to sign the schema_type, maybe this is clearer for describing object
  query :good, type: { name: String, price: Float, spec: { size: String, weight: Integer } }, desc: 'good info'
  query :good_name, type: String # It's also OK, but some superfluous
  query :good_name, String       # recommended
  # About Combined Schema (`one_of` ..), see the link below.

  # method signature
  # usage
  do_query by: {
    search_type: String,
     search_val: String,
        export!: Boolean
  # The same effect as above, but a little bit repetitive
  query  :search_type, String
  query  :search_val, String
  query! :export, Boolean

  # method signature
  # `exp_by` (select_example_by): choose the example fields.
  examples(exp_by = :all, examples_hash)
  # usage
  # it defines 2 examples by using parameter :id and :name
  # if pass :all to `exp_by`, keys will be all the parameter's names.
  examples [:id, :name], {
      :right_input => [ 1, 'user'], # == { id: 1, name: 'user' }
      :wrong_input => [ -1, ''   ]

This trick show you how to define combined schema (by using one_of ..)

>> More About param DSL <<

(4) request_body family methods (OAS - Request Body Object)

OpenAPI 3.0 uses the requestBody keyword to distinguish the payload from parameters.

  body_ref      # for reuse component,
                #   it links sepcified RefObjs (by component keys) to current body.
  body, body!   # alias of request_body
  form, form!   # define a multipart/form-data body
  data          # define [a] property in the form-data body
  file, file!   # define a File media-type body

Bang methods(!) means the specified media-type body is required.

  # method signature
  request_body(required, media_type, data: { }, **options)
  # usage
  # (1) `data` contains all the attributes required by this request body.
  # (2) `param_name!` means it is required, otherwise without '!' means optional.
  request_body :opt, :form, data: { id!: Integer, name: { type: String, desc: 'name' } }, desc: 'form-data'

  # method signature
  # usage
  body_ref :UpdateDogeBody

  # method signature
  body!(media_type, data: { }, **options)
  # usage
  body :json

  # method implement
  def form data:, **options
    body :form, data: data, **options
  # usage
  form! data: {
      name: String,
      password: String,
      password_confirmation: String
  # advance usage
  form data: {
          :name! => { type: String, desc: 'user name' },
      :password! => { type: String, pattern: /[0-9]{6,10}/, desc: 'password' },
      # optional
        :remarks => { type: String, desc: 'remarks' },
  }, exp_by:            %i[ name password ],
     examples: {         #    ↓        ↓
         :right_input => [ 'user1', '123456' ],
         :wrong_input => [ 'user2', 'abc'    ]
  desc: 'for creating a user'

  # method implement
  def data name, type = nil, schema_info = { }
    schema_info[:type] = type if type.present?
    form data: { name => schema_info }
  # usage: please look at the 4th point below

  # about `file`
  def file! media_type, data: { type: File }, **options
    body! media_type, data: data, **options
  1. media_type: we provide some mapping from symbols to real media-types.
  2. schema_info: as above (see param).
  3. exp_by and examples: for the above example, the following has the same effect: examples: { :right_input => { name: 'user1', password: '123456' }, :wrong_input => { name: 'user2', password: 'abc' } }
  4. [IMPORTANT] Each request bodies you declared will FUSION together.
    (1) Media-Types will be merged to requestBody["content"] ruby form data: { }, desc: 'desc' body :json, data: { }, desc: 'desc' # will generate: "content": { "multipart/form-data": { }, "application/json": { } } (2) The same media-types will fusion, but not merge:
    (So that you can write form separately, and make data method possible.) ruby data :param_a!, String data :param_b, Integer # or same as: form data: { :param_a! => String } form data: { :param_b => Integer } # will generate: { "param_a": { "type": "string" }, "param_b": { "type": "integer" } } (call it X) # therefore: # "content": { "multipart/form-data": # { "schema": { "type": "object", "properties": { X }, "required": [ "param_a" ] } # }

(5) response family methods (OAS - Response Object)

Define the responses for the API (action).

  response      # aliases: `resp` and `error`
  # method signature
  response(code, desc, media_type = nil, data: { }, type: nil)
  # usage
  resp 200, 'json response', :json, data: { name: 'test' }
  response 200, 'query result', :pdf, type: File
  # same as:
  response 200, 'query result', :pdf, data: File

  # method signature
  # usage
  response_ref 700 => :AResp, 800 => :BResp

practice: Automatically generate responses based on the agreed error class. AutoGenDoc

(6) Callback (OAS - Callback Object)

About Callbacks

In OpenAPI 3 specs, you can define callbacks – asynchronous, out-of-band requests that your service will send to some other service in response to certain events. This helps you improve the workflow your API offers to clients.
A typical example of a callback is a subscription functionality ... you can define the format of the “subscription” operation as well as the format of callback messages and expected responses to these messages.
This description will simplify communication between different servers and will help you standardize use of webhooks in your API.
Complete YAML Example

The structure of Callback Object:


To define callbacks, you can use callback method:

  # method signature
  callback(event_name, http_method, callback_url, &block)
  # usage
  callback :myEvent, :post, 'localhost:3000/api/goods' do
    query :name, String
    data :token, String
    response 200, 'success', :json, data: { name: String, description: String }

Use runtime expressions in callback_url:

  callback :myEvent, :post, '{body callback_addr}/api/goods/{query id}'
  # the final URL will be: {$request.body#/callback_addr}/api/goods/{$request.query.id}
  # Note: Other expressions outside "$request" are not supported yet

(7) Authentication and Authorization

First of all, please make sure that you have read one of the following documents: OpenApi Auth or securitySchemeObject

##### Define Security Scheme

Use these DSL in your initializer or components block:

  security_scheme # alias `auth_scheme`
  base_auth       # will call `security_scheme`
  bearer_auth     # will call `security_scheme`
  api_key         # will call `security_scheme`

It's very simple to use (if you understand the above document)

  # method signature
  security_scheme(scheme_name, other_info)
  # usage
  security_scheme :BasicAuth, { type: 'http', scheme: 'basic', desc: 'basic auth' }

  # method signature
  base_auth(scheme_name, other_info = { })
  bearer_auth(scheme_name, format = 'JWT', other_info = { })
  api_key(scheme_name, field:, in:, **other_info)
  # usage
  base_auth :BasicAuth, desc: 'basic auth' # the same effect as ↑↑↑
  bearer_auth :Token
  api_key :ApiKeyAuth, field: 'X-API-Key', in: 'header', desc: 'pass api key to header'

##### Apply Security

  # In initializer
  # Global effectiveness
  global_security # alias
  global_auth     # alias

  # In `api`'s block
  # Only valid for the current controller
  security  # alias
  auth      # alias
  need_auth # alias

Name is different, signature and usage is similar.

  # method signature
  security_require(scheme_name, scopes: [ ])
  # usage
  global_auth :Token
  need_auth   :Token
  auth :OAuth, scopes: %w[ read_example admin ]

(8) Overriding Global Servers by server

  # method signature
  server(url, desc: '')
  # usage
  server 'http://localhost:3000', desc: 'local'

DSL methods inside components's block (code source)

(Here corresponds to OAS Components Object)

Inside components's block, you can use the same DSL as [DSL methods inside api and api_dry's block]. But there are two differences:

(1) Each method needs to pass one more parameter component_key (in the first parameter position), this will be used as the reference name for the component.

  query! :UidQuery, :uid, String

This writing is feasible but not recommended, because component's key and parameter's name seem easy to confuse. The recommended writing is:

  query! :UidQuery => [:uid, String]

(2) You can use schema to define a Schema Component.

  # method signature
  schema(component_key, type = nil, **schema_info)
  # usage
  schema :Dog  => [ String, desc: 'dogee' ] # <= schema_type is `String`
  # advance usage
  schema :Dog => [
          id!: Integer,
          name: { type: String, must_be: 'name', desc: 'name' }
      }, # <= this hash is schema type[1]
      dft: { id: 1, name: 'pet' },
      desc: 'dogee'
  # or (unrecommended)
  schema :Dog, { id!: Integer, name: String }, dft: { id: 1, name: 'pet' }, desc: 'dogee'
  # pass a ActiveRecord class constant as `component_key`,
  #   it will automatically read the db schema to generate the component.
  schema User # easy! And the component_key will be :User

[1] see: Type

Run! - Generate JSON Documentation File

Use OpenApi.write_docs:

  # initializer
  OpenApi.write_docs generate_files: !Rails.env.production?

  # or run directly in console
  OpenApi.write_docs # will generate json doc files

Then the JSON files will be written to the directories you set. (Each API a file.)

Use Swagger UI(very beautiful web page) to show your Documentation

Download Swagger UI (version >= 2.3.0 support the OAS3) to your project, change the default JSON file path(url) in index.html. In order to use it, you may have to enable CORS, see


Trick1 - Write the DSL Somewhere Else

Does your documentation take too many lines?
Do you want to separate documentation from controller to simplify both?
Very easy! Just follow

  # config/initializers/open_api.rb
  # in your configuration
  base_doc_classes: [ApiDoc]

  # app/api_doc/api_doc.rb
  require 'open_api/dsl'

  class ApiDoc < Object
    include OpenApi::DSL

  # app/api_doc/v1/examples_doc.rb
  class V1::ExamplesDoc < ApiDoc
    route_base 'api/v1/examples'

    api :index do
      # ...

Explain: These four steps are necessary:

  1. create a class, like ApiDoc, and make it include OpenApi::DSL (then it could be the base class for writing Api spec).
  2. set the specified Api spec's base_doc_classes to ApiDoc.
  3. let your doc class (like V1::ExamplesDoc) inherit the base_doc_classes (ApiDoc).
  4. set the route_base (to route path api/v1/examples of that controller Api::V1::ExamplesController) inside V1::ExamplesDoc.

Notes: file name ends in _doc.rb by default, but you can change it by setting Config.doc_location (it should be file paths, defaults to ./app/**/*_doc.rb).

Trick2 - Global DRYing

Method api_dry is for DRY but its scope is limited to the current controller.

I have no idea of best practices, But you can look at this file.
The implementation of the file is: do api_dry when inherits the base controller inside inherited method.

You can use sort to specify the order of parameters.

Trick3 - Auto Generate Description

  desc 'api desc',
       search_type!: 'search field, allows:<br/>'
  query :search_type, String, enum: %w[name creator category price]

  # or

  query :search_type, String, desc!: 'search field, allows:<br/>',
        enum: %w[name creator category price]

Notice ! use (search_type!, desc!), it tells ZRO to append information that analyzed from definitions (enum, must_be ..) to description automatically.

Any one of above will generate:

search field, allows:
1/ name
2/ creator,
3/ category
4/ price

You can also use Hash to define enum:

  query :view, String, desc: 'allows values<br/>', enum!: {
          'all goods (default)': :all,
                  'only online': :online,
                 'only offline': :offline,
              'expensive goods': :get,
                  'cheap goods': :borrow,

Read this file to learn more.

Trick4 - Skip or Use parameters define in api_dry

Pass skip: [] and use: [] to api like following code:

  api :index, 'desc', skip: [ :Token ]

Look at this file to learn more.

Trick5 - Auto Generate index/show Actions's Response-Types Based on DB Schema

Use method load_schema in api_dry.

See this file for uasge information.

Trick6 - Combined Schema (one_of / all_of / any_of / not)

  query :combination, one_of: [ :GoodSchema, String, { type: Integer, desc: 'integer input' } ]

  form data: {
      :combination_in_form => { any_of: [ Integer, String ] }

  schema :PetSchema => [ not: [ Integer, Boolean ] ]

OAS: link1, link2


  • You wrote document of the current API, but not find in the generated json file?
    Check your routing settings.
  • Undefine method match?
    Monkey patches for String and Symbol: ruby class String # Symbol def match?(pattern); !match(pattern).nil? end end
  • Report error when require routes.rb?*
    1. Run rails routes.
    2. Copy the output to a file, for example config/routes.txt. Ignore the file config/routes.txt.
    3. Put c.rails_routes_file = 'config/routes.txt' to your ZRO config.

About OpenApi.docs and OpenApi.routes_index

After OpenApi.write_docs, the above two module variables will be generated.

OpenApi.docs: A Hash with API names as keys, and documents of each APIs as values.
documents are instances of ActiveSupport::HashWithIndifferentAccess.

OpenApi.routes_index: Inverted index of controller path to API name mappings.
Like: { 'api/v1/examples' => :homepage_api }
It's useful when you want to look up a document based on a controller and do something.



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 rubygems.org.


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

Code of Conduct

Everyone interacting in the Zero-OpenApi project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.