Mocking APIs

Overview

Generate mock API servers from OpenAPI specifications that return realistic, schema-compliant response data for development and testing. Support dynamic response generation with Faker.js data, configurable latency simulation, stateful CRUD behavior, and request recording for contract testing validation.

Prerequisites

• OpenAPI 3.0+ specification file with response schema definitions
• Mock server runtime: Prism (Stoplight), json-server, MSW (Mock Service Worker), or WireMock
• Faker.js or equivalent for realistic test data generation
• Docker for containerized mock server deployment (optional but recommended)
• Frontend or consumer application needing API stubs for parallel development

Instructions

1. Read the OpenAPI specification using Read and extract all endpoint definitions, response schemas, and example values to build the mock response inventory.
2. Generate response fixtures for each endpoint using schema-aware data generation: realistic names (Faker), valid emails, properly formatted dates, and relational IDs that reference other mock entities.
3. Configure the mock server to match requests by method, path pattern, query parameters, and request body content type, returning the appropriate fixture.
4. Add stateful behavior for CRUD operations: POST creates a record in memory, GET returns it, PUT updates it, DELETE removes it -- enabling realistic integration testing flows.
5. Implement configurable response delays (50-500ms per endpoint) to simulate real-world latency and test client timeout handling.
6. Add error scenario mocking: configure specific request patterns to return 400, 401, 404, 429, or 500 responses for testing error handling paths.
7. Enable request recording that captures all incoming requests with timestamps and headers for later replay in contract tests.
8. Create a startup script that launches the mock server on a configurable port with hot-reload when fixture files change.

See ${CLAUDESKILLDIR}/references/implementation.md for the full implementation guide.

Output

• ${CLAUDESKILLDIR}/mocks/server.js - Mock server entry point with route registration
• ${CLAUDESKILLDIR}/mocks/fixtures/ - Per-endpoint response fixture JSON files
• ${CLAUDESKILLDIR}/mocks/generators/ - Dynamic response generators using Faker.js
• ${CLAUDESKILLDIR}/mocks/scenarios/ - Error scenario configurations (4xx, 5xx responses)
• ${CLAUDESKILLDIR}/mocks/state.js - In-memory state store for CRUD behavior
• ${CLAUDESKILLDIR}/mocks/recordings/ - Captured request logs for contract testing
• ${CLAUDESKILLDIR}/docker-compose.mock.yml - Docker configurati