openapi_ruby

A unified OpenAPI toolkit for Rails that combines test-driven spec generation, reusable schema components as Ruby classes, and runtime request/response validation middleware. Supports OpenAPI 3.0 and 3.1. Works with both RSpec and Minitest.

Replaces rswag, rswag-schema-components, and committee with a single gem.

Key Features

OpenAPI 3.0 & 3.1 with JSON Schema 2020-12 (via json_schemer)
Test-framework agnostic — works with RSpec and Minitest
Schema components as Ruby classes with inheritance
Runtime middleware for request/response validation with deep type checking
Strong params derived from schema components
Spec generation from test definitions
Optional Swagger UI via CDN

Requirements

Ruby >= 3.2
Rails >= 7.0

Installation

Add to your Gemfile:

gem "openapi-ruby"

Run the install generator:

rails generate openapi_ruby:install

This creates:

config/initializers/openapi_ruby.rb — configuration
spec/openapi_helper.rb or test/openapi_helper.rb — test helper
app/api_components/ — directory for schema components
swagger/ — output directory for generated specs
Engine mount in config/routes.rb

Configuration

# config/initializers/openapi_ruby.rb
OpenapiRuby.configure do |config|
  config.schemas = {
    public_api: {
      info: { title: "My API", version: "v1" },
      servers: [{ url: "/" }]
    }
  }

  config.component_paths = ["app/api_components"]
  config.camelize_keys = true
  config.schema_output_dir = "swagger"
  config.schema_output_format = :yaml
  config.validate_responses_in_tests = true

  # Runtime middleware (disabled by default)
  config.request_validation = :disabled   # :enabled, :disabled, :warn_only
  config.response_validation = :disabled

  # Optional Swagger UI (disabled by default)
  config.ui_enabled = false
end

OpenAPI Version

The default OpenAPI version is 3.1.0. To generate 3.0.x schemas (e.g., when using nullable: true):

config.schemas = {
  public_api: {
    openapi_version: "3.0.3",
    info: { title: "My API", version: "v1" },
    servers: [{ url: "/" }]
  }
}

Multiple Schemas with Scopes

For projects with multiple APIs, use component_scope to partition components:

config.schemas = {
  "internal/v1/schema": {
    info: { title: "Internal API", version: "v1" },
    component_scope: :internal_v1
  },
  "public/v2/schema": {
    info: { title: "Public API", version: "v2" },
    component_scope: :public_v2
  }
}

# Infer scopes from directory structure (e.g., internal/v1/schemas/user.rb → :internal_v1)
config.component_scope_paths = {
  "internal/v1" => :internal_v1,
  "public/v2" => :public_v2
}

Components are automatically scoped based on their file path. Use shared_component to include a component in all schemas, or component_scopes :scope1, :scope2 to assign explicitly.

Schema Components

Define your API schemas as Ruby classes:

# app/api_components/schemas/user.rb
class Schemas::User
  include OpenapiRuby::Components::Base

  schema(
    type: :object,
    required: %w[id name email],
    properties: {
      id: { type: :integer, readOnly: true },
      name: { type: :string },
      email: { type: :string },
      created_at: { type: [:string, :null], format: "date-time" }
    }
  )
end

Inheritance

class Schemas::AdminUser < Schemas::User
  schema(
    properties: {
      role: { type: :string, enum: %w[admin superadmin] }
    }
  )
end

Child schemas deep-merge with their parent — AdminUser has all of User's properties plus role.

Component Types

class SecuritySchemes::BearerAuth
  include OpenapiRuby::Components::Base
  component_type :securitySchemes

  schema(
    type: :http,
    scheme: :bearer,
    bearerFormat: "JWT"
  )
end

Supported types: schemas, parameters, securitySchemes, requestBodies, responses, headers, examples, links, callbacks.

Key Transformation

By default, snake_case keys are converted to camelCase in the output. Disable globally with config.camelize_keys = false or per-component:

class Schemas::User
  include OpenapiRuby::Components::Base
  skip_key_transformation true
  # ...
end

Scopes

Assign components to scopes for multiple API specs:

class Schemas::AdminUser
  include OpenapiRuby::Components::Base
  component_scopes :admin
  # ...
end

Strong Params

Schema components can derive Rails strong params permit lists:

Schemas::UserInput.permitted_params
# => [:name, :email]

# Handles nested objects and arrays:
# [:title, { tags: [] }, { address: [:street, :city] }]

Use the controller helper:

class Api::V1::UsersController < ActionController::API
  include OpenapiRuby::ControllerHelpers

  def create
    user = User.new(openapi_permit(Schemas::UserInput))
    # ...
  end
end

Works with ActionPolicy — use permitted_params inside your policy's params_filter block.

Component Generator

rails generate openapi_ruby:component User schemas
rails generate openapi_ruby:component BearerAuth security_schemes

Testing with RSpec

# spec/openapi_helper.rb
require "openapi_ruby/rspec"

# spec/requests/users_spec.rb
require "openapi_helper"

RSpec.describe "Users API", type: :openapi do
  path "/api/v1/users" do
    get "List users" do
      tags "Users"
      operationId "listUsers"
      produces "application/json"

      response 200, "returns all users" do
        schema type: :array, items: { "$ref" => "#/components/schemas/User" }

        run_test! do
          expect(JSON.parse(response.body).length).to be > 0
        end
      end
    end

    post "Create a user" do
      tags "Users"
      consumes "application/json"

      request_body required: true, content: {
        "application/json" => {
          schema: { "$ref" => "#/components/schemas/UserInput" }
        }
      }

      response 201, "user created" do
        schema "$ref" => "#/components/schemas/User"
        let(:request_body) { { name: "Jane", email: "jane@example.com" } }
        run_test!
      end

      response 422, "validation errors" do
        schema "$ref" => "#/components/schemas/ValidationErrors"
        let(:request_body) { { name: "" } }
        run_test!
      end
    end
  end

  path "/api/v1/users/{id}" do
    parameter name: :id, in: :path, schema: { type: :integer }, required: true

    get "Get a user" do
      response 200, "user found" do
        schema "$ref" => "#/components/schemas/User"
        let(:id) { User.create!(name: "Jane", email: "jane@example.com").id }
        run_test!
      end

      response 404, "not found" do
        let(:id) { 0 }
        run_test!
      end
    end
  end
end

DSL Reference

Method	Level	Description
`path(template, &block)`	Top	Define an API path
`get/post/put/patch/delete(summary, &block)`	Path	Define an operation
`tags(*tags)`	Operation	Tag the operation
`operationId(id)`	Operation	Set operation ID
`description(text)`	Operation	Operation description
`deprecated(bool)`	Operation	Mark as deprecated
`consumes(*types)`	Operation	Request content types
`produces(*types)`	Operation	Response content types
`security(schemes)`	Operation	Security requirements
`parameter(name:, in:, schema:, **opts)`	Path/Operation	Define a parameter
`request_body(required:, content:)`	Operation	Define request body
`response(status, description, &block)`	Operation	Define expected response
`schema(definition)`	Response	Response body schema
`header(name, schema:, **opts)`	Response	Response header
`run_test!(&block)`	Response	Execute request and validate

Testing with Minitest

# test/test_helper.rb
require "openapi_ruby/minitest"

# test/integration/users_test.rb
require "test_helper"

class UsersApiTest < ActionDispatch::IntegrationTest
  include OpenapiRuby::Adapters::Minitest::DSL

  openapi_schema :public_api

  api_path "/api/v1/users" do
    get "List users" do
      tags "Users"
      produces "application/json"

      response 200, "returns all users" do
        schema type: :array, items: { "$ref" => "#/components/schemas/User" }
      end
    end

    post "Create a user" do
      consumes "application/json"

      request_body required: true, content: {
        "application/json" => {
          schema: { "$ref" => "#/components/schemas/UserInput" }
        }
      }

      response 201, "user created" do
        schema "$ref" => "#/components/schemas/User"
      end
    end
  end

  test "GET /api/v1/users returns users" do
    User.create!(name: "Jane", email: "jane@example.com")

    assert_api_response :get, 200 do
      assert_equal 1, parsed_body.length
    end
  end

  test "POST /api/v1/users creates a user" do
    assert_api_response :post, 201, body: { name: "Jane", email: "jane@example.com" } do
      assert_equal "Jane", parsed_body["name"]
    end
  end
end

Spec Generation

Generate OpenAPI spec files without running tests:

rake openapi_ruby:generate

This uses RSpec --dry-run (or loads Minitest files) to collect API definitions and write schemas. It auto-detects the test framework, or you can set FRAMEWORK=rspec or FRAMEWORK=minitest. Custom patterns: PATTERN="packs/*/spec/**/*_spec.rb".

Schemas are also generated automatically after running the full test suite via after(:suite) / Minitest.after_run hooks.

Runtime Middleware

Validate requests and responses against your OpenAPI spec at runtime:

OpenapiRuby.configure do |config|
  config.request_validation = :enabled    # :enabled, :disabled, :warn_only
  config.response_validation = :enabled
end

The middleware validates:

Requests: parameter types, required parameters, request body schema (required fields, types, constraints like minLength), content types
Responses: body schema with full $ref resolution, required fields, types

Invalid requests return 400 with details. Invalid responses return 500. In :warn_only mode, validation errors are logged but requests pass through.

Strict Mode

Strict mode can be enabled per-schema to return 404 for undocumented paths:

config.schemas = {
  public_api: {
    info: { title: "My API", version: "v1" },
    strict_mode: true  # 404 for undocumented paths
  }
}

Swagger UI

Enable optional Swagger UI:

OpenapiRuby.configure do |config|
  config.ui_enabled = true
end

Visit /api-docs/ui to see your API documentation. Schema files are served at /api-docs/schemas/:name.

Engine Routes

# config/routes.rb
mount OpenapiRuby::Engine => "/api-docs"

License

MIT