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API Documentation Tool

Apipie-rails is a DSL and Rails engine for documenting you RESTful API. Instead of traditional use of #comments, Apipie let's you describe the code by code. This brings advantages like:

  • no need to learn yet another syntax, you already know Ruby, right?
  • possibility reuse the doc for other purposes (such as validation)
  • easier to extend and maintain (no string parsing involved)
  • possibility to use other sources for documentation purposes (such as routes etc.)

The documentation is available right in your app (by default under /apipie path. In development mode, you can see the changes as you go. It's markup language agnostic and even provides an API for reusing the documentation data in form of JSON.

Getting started

The easiest way to get Apipie up and running with your app is:

$ echo "gem 'apipie-rails'" >> Gemfile
$ bundle install
$ rails g apipie:install

Now you can start documenting your resources and actions (see DSL Reference for more info:

api :GET, '/users/:id'
param :id, :number
def show
  # ...

Run your application and see the result at http://localhost:3000/apipie. For it's further processing, you can use http://localhost:3000/apipie.json.

For more comprehensive getting started guide, see this demo, that includes features such as generating documenation from tests, recording examples etc.



Pajk and iNecas


See Contributors page. Special thanks to all of them!


Apipie-rails is released under the MIT License


DSL Reference

Resource Description

You can describe a resource on controller level. The description is introduced by calling resource_description do ... end.

Inheritance is supported, so you can specify common params for group of controllers in their parent class.

The following keywords are available (all are optional):

How will the resource be referenced in Apipie (paths, see command etc.), by default controller_name.downcase is used.
Human readable name of resource. By default is used.
short (also short_description)
Short description of the resource (it's shown on both list of resources and resource details)
desc (also description and full_description)
Full description of the resource (shown only in resource details)
Common params for all methods defined in controller/child controllers.
What url is the resource available under.
api_versions (also api_version)
What versions does the controller define the resource. (See Versioning for details.)
request / response formats.
Describe every possible error that can happen what calling all methods defined in controller. HTTP response code and description can be provided.
In case of versioning, this sets app info description on per_version basis.


resource_description do
  short 'Site members'
  path '/users'
  formats ['json']
  param :id, Fixnum, :desc => "User ID", :required => false
  param :resource_param, Hash, :desc => 'Param description for all methods' do
    param :ausername, String, :desc => "Username for login", :required => true
    param :apassword, String, :desc => "Password for login", :required => true
  api_version "development"
  error 404, "Missing"
  error 500, "Server crashed for some <%= reason %>"
  description <<-EOS
    == Long description
     Example resource for rest api documentation
     These can now be accessed in <tt>shared/header</tt> with:
       Headline: <%= headline %>
       First name: <%= person.first_name %>

     If you need to find out whether a certain local variable has been
     assigned a value in a particular render call, you need to use the
     following pattern:

     <% if local_assigns.has_key? :headline %>
        Headline: <%= headline %>
     <% end %>

    Testing using <tt>defined? headline</tt> will not work. This is an
    implementation restriction.

    === Template caching

    By default, Rails will compile each template to a method in order
    to render it. When you alter a template, Rails will check the
    file's modification time and recompile it in development mode.

Method Description

Then describe methods available to your API.

Say how is this method exposed and provide short description. The first parameter is HTTP method (one of :GET/:POST/:PUT/:DELETE). The second parameter is relative URL path which is mapped to this method. The last parameter is methods short description. You can use this +api+ method more than once for one method. It could be useful when there are more routes mapped to it.
api_versions (also api_version)
What version(s) does the action belong to. (See Versioning for details.)
Look at Parameter description section for details.
Method level request / response formats.
Describe each possible error that can happen what calling this method. HTTP response code and description can be provided.
Full method description which will be converted to HTML by chosen markup language processor.
Provide example of server response, whole communication or response type. It will be formatted as code.
Provide reference to another method, this has to be string with controller_name#method_name.


api :GET, "/users/:id", "Show user profile"
error :code => 401, :desc => "Unauthorized"
error :code => 404, :desc => "Not Found"
param :session, String, :desc => "user is logged in", :required => true
param :regexp_param, /^[0-9]* years/, :desc => "regexp param"
param :array_param, [100, "one", "two", 1, 2], :desc => "array validator"
param :boolean_param, [true, false], :desc => "array validator with boolean"
param :proc_param, lambda { |val|
  val == "param value" ? true : "The only good value is 'param value'."
}, :desc => "proc validator"
description "method description"
formats ['json', 'jsonp', 'xml']
example " 'user': {...} "
see "users#showme", "link description"
see :link => "users#update", :desc => "another link description"
def show

Parameter Description

Use param to describe every possible parameter. You can use Hash validator in cooperation with block given to param method to describe nested parameters.

The first argument is parameter name as a symbol.
Second parameter is parameter validator, choose one from section Validators
Parameter description.
Set this true/false to make it required/optional. Default is optional
Set true is nil can be passed for this param.


param :user, Hash, :desc => "User info" do
  param :username, String, :desc => "Username for login", :required => true
  param :password, String, :desc => "Password for login", :required => true
  param :membership, ["standard","premium"], :desc => "User membership"
def create

DRY with param_group

Often, params occur together in more actions. Typically, most of the params for create and update actions are common for both of them.

This params can be extracted with def_param_group and param_group keywords.

The definition is looked up in the scope of the controller. If the group is defined in a different controller, it might be referenced by specifying the second argument.


# v1/users_controller.rb
def_param_group :address do
  param :street, String
  param :number, Integer
  param :zip, String

def_param_group :user do
  param :user, Hash do
    param :name, String, "Name of the user"
    param_group :address

api :POST, "/users", "Create an user"
param_group :user
def create
  # ...

api :PUT, "/users/:id", "Update an user"
param_group :user
def update
  # ...

# v2/users_controller.rb
api :POST, "/users", "Create an user"
param_group :user, V1::UsersController
def create
  # ...

Action Aware params

In CRUD operations, this pattern occurs quite often: params that need to be set are:

  • for create action: required => true and allow_nil => false
  • for update action: required => false and allow_nil => false

This makes it hard to share the param definitions across theses actions. Therefore, you can make the description a bit smarter by setting :action_aware => true.

You can specify explicitly how the param group should be evaluated with :as option (either :create or :update)


def_param_group :user do
  param :user, Hash, :action_aware => true do
    param :name, String, :required => true
    param :description, :String

api :POST, "/users", "Create an user"
param_group :user
def create
  # ...

api :PUT, "/users/admin", "Create an admin"
param_group :user, :as => :create
def create_admin
  # ...

api :PUT, "/users/:id", "Update an user"
param_group :user
def update
  # ...

In this case, user[name] will be not be allowed nil for all actions and required only for create and create_admin. Params with allow_nil set explicitly don't have this value changed.

Action awareness is being inherited from ancestors (in terms of nested params).


Sometimes, the actions are not defined in the controller class directly but included from a module instead. You can load the Apipie DSL into the module by extending it with Apipie::DSL::Concern.

The module can be used in more controllers. Therefore there is a way how to substitute parts of the documentation in the module with controller specific values. The substitutions can be stated explicitly with apipie_concern_subst(:key => "value") (needs to be called before the module is included to take effect). The substitutions are performed in paths and descriptions of APIs and names and descriptions of params.

There are some default substitutions available:

value of controller.controller_path, e.g. api/users for Api::UsersController
Apipie identifier of the resource, e.g. users for Api::UsersController or set by resource_id


# users_module.rb
module UsersModule
  extend Apipie::DSL::Concern

  api :GET, '/:controller_path', 'List :resource_id'
  def index
    # ...

  api :GET, '/:resource_id/:id', 'Show a :resource'
  def show
    # ...

  api :POST, '/:resource_id', "Create a :resource"
  param :concern, Hash, :required => true
    param :name, String, 'Name of a :resource'
    param :resource_type, ['standard','vip']
  def create
    # ...

  api :GET, '/:resource_id/:custom_subst'
  def custom
    # ...

# users_controller.rb
class UsersController < ApplicationController

  resource_description { resource_id 'customers' }

  apipie_concern_subst(:custom_subst => 'custom', :resource => 'customer')
  include UsersModule

  # the following paths are documented
  # api :GET, '/users'
  # api :GET, '/customers/:id', 'Show a customer'
  # api :POST, '/customers', 'Create a customer'
  #   param :customer, :required => true do
  #     param :name, String, 'Name of a customer'
  #     param :customer_type, ['standard', 'vip']
  #   end
  # api :GET, '/customers/:custom'

Configuration Reference

Create configuration file in e.g. /config/initializers/apipie.rb. You can set application name, footer text, API and documentation base URL and turn off validations. You can also choose your favorite markup language of full descriptions.

Name of your application used in breadcrumbs navigation.
Copyright information (shown in page footer).
Documentation frontend base url.
Base url of your API, most probably /api.
Default API version to be used (1.0 by default)
Parameters validation is turned off when set to false.
Application long description.
Set to enable/disable reloading controllers (and the documentation with it), by default enabled in development.
For reloading to work properly you need to specify where your API controllers are.
You can choose markup language for descriptions of your application, resources and methods. RDoc is the default but you can choose from or In order to use Markdown you need Redcarpet gem and for Textile you need RedCloth. Add those to your gemfile and run bundle if you want to use them. You can also add any other markup language processor.
Name of a layout template to use instead of Apipie's layout. You can use Apipie.include_stylesheets and Apipie.include_javascripts helpers to include Apipie's stylesheets and javascripts.
An array of controller names (strings) (might include actions as well) to be ignored when generationg the documentation e.g. %w[Api::CommentsController Api::PostsController#post]
Use controller paths instead of controller names as resource id. This prevents same named controllers overwriting each other.


Apipie.configure do |config|
  config.app_name = "Test app"
  config.copyright = "&copy; 2012 Pavel Pokorny"
  config.doc_base_url = "/apidoc"
  config.api_base_url = "/api"
  config.validate = false
  config.markup =
  config.reload_controllers = true
  config.api_controllers_matcher = File.join(Rails.root, "app", "controllers", "**","*.rb")
  config.app_info = "
    This is where you can inform user about your application and API
    in general.
  ", '1.0'


Every parameter needs to have associated validator. For now there are some basic validators. You can always provide your own to reach complex results.

If validations are enabled (default state) the parameters of every request are validated. If the value is wrong a +ArgumentError+ exception is raised and can be rescued and processed. It contains some description of parameter value expectations. Validations can be turned off in configuration file.


Check the parameter type. Only String, Hash and Array are supported for the sake of simplicity. Read more to to find out how to add your own validator.

param :session, String, :desc => "user is logged in", :required => true
param :facts, Hash, :desc => "Additional optional facts about the user"


Check parameter value against given regular expression.

param :regexp_param, /^[0-9]* years/, :desc => "regexp param"


Check if parameter value is included given array.

param :array_param, [100, "one", "two", 1, 2], :desc => "array validator"


If you need more complex validation and you know you won't reuse it you can use Proc/lambda validator. Provide your own Proc taking value of parameter as the only argument. Return true if value pass validation or return some text about what is wrong. _Don't use the keyword return if you provide instance of Proc (with lambda it is ok), just use the last statement return property of ruby.

param :proc_param, lambda { |val|
  val == "param value" ? true : "The only good value is 'param value'."
}, :desc => "proc validator"


You can describe hash parameters in depth if you provide a block with description of nested values.

param :user, Hash, :desc => "User info" do
  param :username, String, :desc => "Username for login", :required => true
  param :password, String, :desc => "Password for login", :required => true
  param :membership, ["standard","premium"], :desc => "User membership"


In fact there is any NilValidator but setting it to nil can be used to override parameters described on resource level.

param :user, nil
def destroy

Adding custom validator

Only basic validators are included but it is really easy to add your own. Create new initializer with subclass of Apipie::Validator::BaseValidator. Two methods are required to implement - instance method <tt>validate(value)</tt> and class method <tt>build(param_description, argument, options, block)</tt>.

When searching for validator +build+ method of every subclass of Apipie::Validator::BaseValidator is called. The first one whitch return constructed validator object is used.

Example: Adding IntegerValidator

We want to check if parameter value is an integer like this:

param :id, Integer, :desc => "Company ID"

So we create apipie_validators.rb initializer with this content:

class IntegerValidator < Apipie::Validator::BaseValidator

  def initialize(param_description, argument)
    @type = argument

  def validate(value)
    return false if value.nil?
    !!(value.to_s =~ /^[-+]?[0-9]+$/)

  def, argument, options, block)
    if argument == Integer || argument == Fixnum, argument)

  def description
    "Must be #{@type}."

Parameters of the build method:

Instance of Apipie::ParamDescription contains all given informations about validated parameter.
Specified validator, in our example it is +Integer+
Hash with specified options, for us just {:desc => "Company ID"}
Block converted into Proc, use it as you desire. In this example nil.


Every resource/method can belong to one or more versions. The version is specified with the api_version DSL keyword. When not specified, the resource belong to config.default_version ("1.0" by default)

resource_description do
  api_versions "1", "2"

api :GET, "/api/users/"
api_version "1"
def index
  # ...

In the example above we say the whole controller/resource is defined for versions "1" and "2", but we override this with explicitly saying index belongs only to version "1". Also inheritance works (therefore we can specify the api_version for the parent controller and all children will know about that).

From the Apipie API perspective, the resources belong to version. With versioning, there are paths like this provided by apipie:


When not specifying the version explicitly in the path (or in dsl), default version (Apipie.configuration.default_version) is used instead ("1.0" by default). Therefore, the application that doesn't need versioning should work as before.

The static page generator takes version parameter (or uses default).

You can specify the versions for the examples, with versions keyword. It specifies the versions the example is used for. When not specified, it's shown in all versions with given method.

When referencing or quering the resource/method descripion, this format should be used: "verson#resource#method". When not specified, the default version is used instead.


The default markup language is RDoc. It can be changed in config file (config.markup=) to one of these:

Use You need Maruku gem.
Use You need RedCloth gem.

Or provide you own object with to_html(text) method. For inspiration this is how Textile markup usage looks like:

class Textile
  def initialize
    require 'RedCloth'
  def to_html(text)

Static files

To generate static version of documentation (perhaps to put it on project site or something) run rake apipie:static task. It will create set of html files (multi-pages, single-page, plain) in your doc directory. By default the documentation for default API version is used, you can specify the version with rake apipie:static[2.0]

When you want to avoid any unnecessary computation in production mode, you can generate a cache with rake apipie:cache and configure the app to use it in production with config.use_cache = Rails.env.production?

Tests Integration

Apipie integrates with automated testing in two ways. Documentation bootstrapping and examples recording.

Documentation Bootstrapping

Let's say you have an application without REST API documentation. However you have a set of tests that are run against this API. A lot of information is already included in this tests, it just needs to be extracted somehow. Luckily, Apipie provides such a feature.

When running the tests, set the APIPIE_RECORD=params environment variable. You can either use it with functional tests

APIPIE_RECORD=params rake test:functionals

or you can run your server with this param, in case you run the tests against running server

APIPIE_RECORD=params rails server

When the process quits, the data from requests/responses are used to determine the documentation. It's quite raw, but it makes the initial phase much easier.

Examples Recording

You can also use the tests to generate up-to-date examples for your code. Similarly to the bootstrapping, you can use it with functional tests or a running server, setting APIPIE_RECORD=examples

APIPIE_RECORD=examples rake test:functionals
APIPIE_RECORD=examples rails server

The data are written into doc/apipie_examples.yml. By default, only the first example is shown for each action. You can customize this by setting show_in_doc attribute at each example.

Bindings Generator

In earlier versions (<= 0.0.13), there was a simple client generator as a part of Apipie gem. As more features and users came to Apipie, more and more there was a need for changes on per project basis. It's hard (or even impossible) to provide a generic solution for the client code. We also don't want to tell you what's the rigth way to do it (what gems to use, how the API should look like etc.).

Therefore you can't generate a client code directly by a rake task in further versions.

There is, however, even better and more flexible way to reuse your API documentation for this purpose: using the API the Apipie provides in the generator code. You can inspire by Foreman API bindings that use exactly this approach. You also don't need to run the service, provided it uses Apipie as a backend.

And if you write one on your own, don't hesitate to share it with us!

Disqus Integration

You can get a Disqus discussion for the right into your documentation. Just set the credentials in Apipie configuration:

config.disqus_shortname = "MyProjectDoc"

External References

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