API Mock Server Config Generator

A mock server simulates a real API without any backend infrastructure. During frontend development, you often need API responses before the real server is ready — mock servers let you build and test UI components against predictable data. They also help QA teams write tests without hitting production databases, and let teams work in parallel without blocking on backend completion.

JSON Server is a zero-code REST API built from a single db.json file. You run npx json-server db.json and instantly get full CRUD endpoints with filtering, sorting, and pagination. It's ideal for rapid prototyping and local development when you want real HTTP requests. The generated db.json from this tool seeds your initial data and resource structure so JSON Server knows what collections to serve.

MSW intercepts network requests at the Service Worker layer in the browser (or at the Node.js http module in tests). Unlike JSON Server, MSW runs inside your app without a separate process. It's the preferred choice for component tests with Vitest or Jest, Storybook stories, and CI environments. MSW handlers are TypeScript functions that return structured responses using the http and HttpResponse API from msw v2.

JSON Server output is a db.json file — a plain object whose top-level keys become REST resource collections. GET /users returns db.json.users, POST /users appends to it, and so on. MSW output is TypeScript source code that exports a handlers array. Each handler is a function that matches method + path and returns an HttpResponse. JSON Server is a standalone dev server; MSW is a library integrated into your test or app code.

MSW v2 uses path patterns identical to Express-style routing. Static paths like /users match exactly. Parameterized paths like /users/:id capture the segment as request.params.id. Wildcard segments and nested paths are both supported. The generated handlers pass through request.params so you can return different response bodies based on the captured ID or other parameters.

No — both JSON Server and MSW are development and testing tools only. JSON Server has no auth, rate limiting, or persistence beyond the flat JSON file. MSW handlers replace real network calls, so they must be disabled before shipping. The standard pattern is to register MSW only when process.env.NODE_ENV === 'test' or when a VITE_MOCK_API flag is set, and never bundle mock handlers into your production build.