Awesome

acts_as_api makes creating XML/JSON responses in Rails 3, 4, 5 and 6 easy and fun.

It provides a simple interface to determine the representation of your model data, that should be rendered in your API responses.

In addition to Rails it theoretically can be used with any ruby app and any database (ActiveRecord, Mongoid and ActiveResource are supported out of the box) as it only has few dependencies.

The lib is very fast in generating your responses and battle tested in production with platforms like Diaspora or flinc.

Introduction

acts_as_api enriches the models and controllers of your app in a Rails-like way so you can easily determine how your API responses should look like:

class User < ActiveRecord::Base

  acts_as_api

  api_accessible :public do |template|
    template.add :first_name
    template.add :age
  end
  # will render json: { "user": { "first_name": "John", "age":  26 } }

  api_accessible :private, extend: :public do |template|
    template.add :last_name
    template.add :email
  end
  # will render json: { "user": { "first_name": "John", "last_name": "Doe", "age":  26, "email": "john@example.org" } }

end

Getting started

A nice introduction about acts_as_api with examples can be found here:

http://fabrik42.github.com/acts_as_api

See the Wiki for a lot of usage examples and features:

https://github.com/fabrik42/acts_as_api/wiki

There are a lot of how-tos like:

Features:

DRY templates for your api responses
Ships with support for ActiveRecord and Mongoid
Support for Rails 3/4 Responders (extracted to responders gem since Rails 5)
Plays very well together with client libs like Backbone.js, RestKit (iOS) or gson (Android).
Easy but very flexible syntax for defining the templates
XML, JSON and JSON-P support out of the box, easy to extend
Minimal dependecies (you can also use it without Rails)
Supports multiple api rendering templates per model. This is especially useful for API versioning or for example for private vs. public access points to a user’s profile.

Requirements:

ActiveModel (>= 3.0.0)
ActiveSupport (>= 3.0.0)
Rack (>= 1.1.0)

Downwards Compatibility