Generate Realistic API Mocks

Covers a 10-step API mocking implementation. Mock server setup - a FastAPI-based MockAPIServer wiring three middleware layers: adding X-Mock-Server and X-Mock-Scenario response headers, simulating configurable network latency per path, and tracking every request's method, path, headers, and timestamp for later verification - plus a catch-all dynamic route matching incoming requests against loaded mock definitions. Request and response stubbing via a StubbingEngine that matches incoming requests against registered stubs by method, path, and a configurable set of matchers (path parameters, query parameters, headers, and body with an exact or partial match type), each stub carrying a priority for resolving overlapping matches, an optional call-count limit, a response delay, and a named scenario, plus a dynamic-stub variant that generates its response from a callback instead of a static template. Dynamic data generation, and mock scenarios for switching server behavior (success, error, slow-response states) at runtime. Contract testing - a ContractMockServer that loads an OpenAPI or AsyncAPI contract, parses its endpoints and schemas, and auto-generates mocks per path, method, and status code directly from the specification's response schemas and request-body validation rules, so the mock server stays synchronized with the real contract instead of being hand-maintained separately. Performance testing against the mock server, mock data management, testing-framework integration (a pytest conftest.py fixture wiring the mock server into a test suite), mock server deployment (a docker-compose.yml for local mock services and a Kubernetes deployment manifest for shared environments), and auto-generated mock documentation (an Overview, Available Endpoints, Scenarios, Data Models, Usage Examples, and Configuration section built per-endpoint from the loaded mock definitions).

Use it when setting up a mock API server, generating mocks from an existing OpenAPI contract, testing against simulated latency or failure scenarios, or deploying a mock server for shared test environments. Skip it for anything unrelated to API mocking or outside this scope.

Input is an API to mock, either hand-specified or an existing OpenAPI or AsyncAPI contract; output is a running mock server with request tracking and configurable scenarios, or, from a contract, an auto-generated mock set that stays in sync with the real API's schemas.

FastAPI for the mock server itself, OpenAPI and AsyncAPI as the contract source for auto-generated mocks, pytest for test-framework integration, and Docker Compose or Kubernetes for deploying the mock server to shared environments.

Engineers testing against an API dependency who need a contract-synchronized mock server with latency simulation and request verification rather than hand-written stub responses that drift from the real API. Also fits validating an API contract before backend completion, or building a demo environment with realistic responses instead of hand-rolled fixtures.