HTTP Mock Server Config Generator

MSW intercepts network requests at the service worker level in browsers, or using a custom Node server in tests. It lets you mock REST and GraphQL APIs without changing application code. It's the most popular choice for frontend integration tests with React Testing Library or Vitest.

json-server creates a full fake REST API from a JSON file in about 30 seconds. It auto-generates CRUD endpoints for each resource in your db.json. Ideal for rapid prototyping and frontend development when the real backend isn't ready yet.

WireMock is a flexible API mocking tool available as a standalone server or Java library. It's popular in Java/Spring ecosystems and enterprise environments. It supports request matching by URL, method, headers, and body, as well as response templating and stateful behavior.

Use MSW for frontend testing (Jest/Vitest + Testing Library) — it intercepts fetch/XHR at the browser level with zero configuration changes. Use json-server for development mocking when you need a quick REST API with CRUD operations accessible from any tool (browser, curl, Postman). Use WireMock for Java/enterprise environments or when you need complex request matching and stateful scenarios.

Set the delay field (in milliseconds) on each route. This is useful for testing loading states, skeleton screens, and timeouts in your application. MSW uses the delay() helper from the msw package. json-server supports a global --delay flag. WireMock uses fixedDelayMilliseconds per mapping.