Build Tag

An HTTP API DSL on top of Sinatra.


Add this line to your application's Gemfile:

gem 'api_sim'

And then execute:

$ bundle

Or install it yourself as:

$ gem install api_sim

Example usage

require 'api_sim'

ENDPOINT_JSON_SCHEMA = {type: "object", properties: {a: {type: "integer"}}}.to_json

app = ApiSim.build_app do
  configure_endpoint 'GET', '/endpoint', 'Hi!', 200, {'X-CUSTOM-HEADER' => 'easy as abc'}, ENDPOINT_JSON_SCHEMA

  configure_dynamic_endpoint 'GET', '/dynamic', ->(req) {
    [201, {'X-CUSTOM-HEADER' => '123'}, 'Howdy!']

  configure_matcher_endpoint 'POST', '/soap', {
    /Operation1/ => [200, {'Content-Type' => 'text/xml+soap'}, '<xml>Response1</xml>'],
    /Operation2/ => [500, {'Content-Type' => 'text/xml+soap'}, '<xml>Response2</xml>'],

run app

The above is an exact copy of the basic/config.ru from the examples. You can boot this without too much effort by running:

cd examples/basic && bundle check || bundle install && bundle exec rackup -I../../lib

After which the simulators should be running on port 9292.


API Sim has an HTTP API that allows you, the developer, to manage responses and verify requests.

The "Request/Response" API

Modify the response from an endpoint

The star in the path should match the request path that you want to update. The "method" in the PUT request should match the HTTP method for the request.

HTTP/1.1 PUT /response/*
  "method": "post",
  "status": 999,
  "body": "{\"id\": 99}",
  "headers": {"NEW-HEADER": "output"}

Read requests made to an endpoint

The star in the path should match the path that you want to retrieve requests for.

GET /requests/:method/*
HTTP/1.1 200 OK



The API that these simulators generate can get pretty smart. To help you, the user, distinguish between failures and "smarts", we've made up an HTTP status code: 498. This code means "we received a request that did not match an expected schema". If you provide the simulators with a request schema for an endpoint, all requests must match that schema. If they do not, they'll receive our fictional status code.


The simulator application has a UI for manipulating and monitoring requests and responses. You can view this UI by visiting /ui at the URL of the simulator.

Additionally, you can configure the endpoint for viewing the UI by adding to your config.ru.

ui_root '/path/to/ui'


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.


Bug reports and pull requests are welcome on GitHub at https://github.com/dugancathal/api_sim.