Dynamic Ruby API Client from Swagger JSON Spec
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Latest commit 75abb1a Dec 22, 2017



Svelte is a Swagger-to-Ruby object mapper.

It reads a Swagger specification file in JSON, and automatically generates Resource Classes with static methods to represent the various HTTP endpoints.

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Add this line to your application's Gemfile:

gem "svelte"

And then execute:

$ bundle

Or install it yourself as:

$ gem install svelte


Point a service at an actual API spec.

You may pass in a URL pointing to a Swagger spec or the JSON directly:

service = Svelte::Service.create(url: "http://path/to/swagger/spec/resource.json", module_name: 'PetStore')
service = Svelte::Service.create(json: "{ <JSON here> }", module_name: 'PetStore')

This will build a dynamically generated client on top of Svelte::Service::PetStore.

The structure of the new module will be based on the API paths and their respective operations. Let's look at an example. Using the complete PetStore spec, we can find the following path:

"/pet/findByStatus": {
  "get": {
    "tags": [
    "summary": "Finds Pets by status",
    "description": "Multiple status values can be provided with comma separated strings",
    "operationId": "findPetsByStatus",
    "produces": [
    "parameters": [
        "name": "status",
        "in": "query",
        "description": "Status values that need to be considered for filter",
        "required": true,
        "type": "array",
        "items": {
          "type": "string",
          "enum": [
          "default": "available"
        "collectionFormat": "multi"
    "responses": {
      "200": {
        "description": "successful operation",
        "schema": {
          "type": "array",
          "items": {
            "$ref": "#/definitions/Pet"
      "400": {
        "description": "Invalid status value"
    "security": [
        "petstore_auth": [

The path contains two parts: pet and findByStatus. This will generate the following hierarchy in the new module:


We can see the path has one get operation. A method will be generated in the FindByStatus module based on the operationId Swagger attribute, which will have the following signature:

  request_options = {}

Where request_payload is a Hash representing the parameters of the operation and request_options, defaulting to an empty Hash, will be a Hash of options to pass to the request.

In our case, the parameters would look like this:

request_parameters = {
  status: ['available', 'pending']


Svelte will return a Faraday::Request object as a response to a call.


Svelte also provides generators for Swagger models. They allow an easy way to programmatically create and validate requests. They also provide an as_json that will generate a valid json body for a given request.

Consider the definitions key of this Swagger model:

  "definitions": {
    "MoneyView": {
      "id": "MoneyView",
      "description": "",
      "required": [
      "extends": "",
      "properties": {
        "amount": {
          "type": "number",
          "format": "double",
          "description": "Decimal amount"
        "currencyCode": {
          "type": "string",
          "description": "ISO 3 letter currency code"

In Svelte you can generate the ruby mapper like this:

class MoneyRequest
  extend Svelte::ModelFactory

view = MoneyRequest::MoneyView.new
view.valid? # false
view.validate # {"currencyCode"=>"Invalid parameter: Missing required parameter", "amount"=>"Invalid parameter: Missing required parameter"}
view.currencyCode = "GBP"
view.amount = 40.00
view.valid? # true
view.as_json # {:currencyCode=>"GBP", :amount=>40.0}


You can specify a timeout option on a per request basis. If the request times out a Svelte::TimeoutError exception will be raised.

  Svelte::Service::PetStore::Pet::FindByStatus.find_pets_by_status(request.as_json, { timeout: 10 })
rescue Svelte::TimeoutError => e

## Limitations

Svelte is still a work in progress gem and it lacks some features that will be implemented in the future. Feel free to request or comment on what you'd like to see supported. Here is a non exhaustive list of the pitfalls we've identified so far:

  • Supports application/json request and response types only
  • API calls return a raw [Faraday::Response] objects. We'll support returning dynamically generated model responses based on the Swagger spec response schema
  • Request parameter validation is only done for url based parameters. It'd be possible to add validations to all parameters of the request. In fact the ModelFactory already provides that functionality, but it requires the client to call valid? on the requests to perform the validation. This should happen automatically


After checking out the repo, run bin/setup to install dependencies. Then, 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 to create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.


  1. Fork it ( https://github.com/notonthehighstreet/svelte/fork )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request