Mockoon — Free Desktop Mock Server

Mockoon is a free desktop application that lets you create local mock HTTP servers in seconds. The problem it solves is frontend-backend coupling: when a frontend team is building a feature but the backend API is not yet implemented, development blocks. Mockoon lets you define the API contract (routes, response shapes, status codes) and run a real local HTTP server immediately — so frontend development and API testing can proceed without waiting for the real backend. It also helps with third-party API dependencies: if you depend on a paid or rate-limited external API, you can mock it locally.

WireMock is a Java-based mock server typically used in backend integration testing, configured via JSON stub files or Java code. It is powerful for complex scenarios but requires Java, has steeper configuration, and is more complex to set up for quick frontend development. Mockoon is a desktop GUI application with a visual drag-and-drop interface — no code required to define routes. It also has a CLI (mockoon-cli) for CI/CD use. Mockoon is better suited for frontend developers who want a quick visual tool; WireMock is better for Java backend teams doing programmatic test automation.

Install the CLI with npm install -g @mockoon/cli. Export your environment from the Mockoon Desktop app as a JSON file and commit it to your repository. In your CI pipeline, run mockoon-cli start --data my-api.json --port 3001 before your tests. The process stays running so your tests can make real HTTP requests to localhost:3001. After tests complete, stop the process. The Mockoon CLI supports Docker — the official image is mockoon/cli — which is ideal for containerized CI environments.

Response rules let you serve different responses for the same route based on request properties like headers, body content, query parameters, or route parameters. For example, you can return a 200 response when a header X-User-Role is admin, and a 403 response otherwise. Rules are evaluated in order, and the first matching rule wins. This makes it possible to simulate different API behaviors (authenticated vs unauthenticated, found vs not found) without creating separate routes.

Data buckets are reusable, in-memory data stores in Mockoon. You define a named bucket with an initial JSON value (which can use Handlebars/Faker templating). Routes can read from and write to buckets using the dataRaw and setData helpers, simulating a stateful API. This means you can mock a full CRUD API: a POST creates an item in the bucket, a GET reads from it, a DELETE removes it — and the data persists across requests during the server session. Data buckets reset to their initial values when the server restarts.

Yes. Mockoon supports TLS/HTTPS for mock servers. In the environment settings you can enable HTTPS, and Mockoon will generate a self-signed certificate automatically. You can also provide your own certificate and key files. This is useful when your application code enforces HTTPS-only requests or when you need to test TLS-specific behavior. In the CLI, pass --https to enable it. Remember to configure your HTTP client to trust the self-signed cert (or disable cert verification in development).