What is API Mocking? — UK Software Development Guide
Direct Answer
API mocking is the practice of simulating an API's behaviour in a test or development environment, without calling the real API. API mocks return predefined responses for given inputs, enabling: frontend development to proceed before the backend API is built, testing of error handling (by mocking API error responses), integration testing without calling external services that have rate limits or costs, and CI/CD testing without external dependencies.
Api-mocking in the UK
API mocking has specific UK government API development value. HMRC MTD, NHS APIs, Companies House, and GOV.UK Pay all provide official sandbox environments — the nearest thing to "real mocks." For development environments (local machine, CI/CD), ClickMasters uses MSW (Mock Service Worker) for frontend mocking and WireMock or Nock for backend API mocking. UK GDPR: API mocks used in development and testing must never contain real personal data — use synthetic data generators (Faker.js, Python Faker) to create realistic but fake response data.
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