Seahorse is a way to describe your API
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Gemfile.lock Initial commit Apr 29, 2013


Seahorse is a way to describe your service APIs as first-class citizens with a declarative DSL. The library also provides Ruby on Rails integration so that take advantage of your API model in controller actions.


Seahorse provides the ability to define an API model, but also has functionality to support parameter validation and serialization of inputs and outputs to API calls. With Rails integration, this is automatic, namely, parameters in params are automatically type-converted and validated, outputs are automatically serialized from your API model to JSON or XML. You can also hook this up to a Sinatra app with a little amount of work.


gem install seahorse


Using Seahorse in a Rails app is pretty easy!

First, define your API model and operations by creating a class like Api::Post in app/models/api/post.rb and including Seahorse::Model:

class Api::Post
  include Seahorse::Model

  # Define a type so you can re-use this later
  type :post do
    model ::Post # Hook up to an AR model
    integer :post_id, as: :id
    string :username, as: [:user, :username]
    string :body
    timestamp :created_at

  # The 'index' action in Rails.
  # Also maps to the 'list_posts' command as an RPC call
  operation :index do
    # Define this if you need to map parameters in the URL
    url '/:username/posts'

    # Define some input parameters
    input do
      string :username, uri: true, required: true
      integer :page

    # Define the output parameters
    output do
      # A list of posts
      list(:posts) { post }

      # The page number of the next page
      integer :next_page

  # Other operations here...

You can generate a JSON description of this API model by calling:

puts Api::Post.to_json

Rails Integration

In Rails, you can hook this API model up to routing by adding the following line in your config/routes.rb:


This finds all API models defined and hooks them up to your Rails app. Note that in Rails, the Post API model will route to your PostsController.

Then you just write Rails code as normal. Here is what the index controller action might look like on PostsController:

class PostsController < ApplicationController
  # You need to add this for Seahorse integration
  include Seahorse::Controller

  def index
    # Simple pagination logic
    page_size, page = 20, params[:page] || 1
    offset = (page - 1) * page_size

    # Build the response
    output = { posts: Post.limit(page_size).offset(offset) }
    output[:next_page] = page + 1 if Post.count > (offset + page_size)


Note that params[:page] can be used without calling .to_i because Seahorse already typecasted it to an integer, since your model's input defined it as one. You no longer have to worry about typecasting values in and out. You simply take input params and call respond_with on the data you want to serialize out the data you want to display (also defined in your API model).

Here's what a create action might look like:

def create
  user = User.where(username: params[:username]).first
  respond_with user.posts.create(params[:post])

Note that all your parameters are automatically validated and type-converted according to the inputs you defined in your API model. You don't have to white list attributes in your model, and you don't need to define strong parameters either; Seahorse does this all for you.


Feel free to open issues or submit pull requests with any ideas you can think of to make integrating the Seahorse model into your application an easier process. This project was initially created as a tech demo for RailsConf 2013 to illustrate some of the principles used to design the client-side SDKs at Amazon Web Services, so the current breadth of features is fairly minimal. Feature additions and extra work on the project is welcome!


Seahorse uses the Apache 2.0 License. See LICENSE for details.