Mockoon is a free, open-source tool that allows you to create and run mock REST APIs locally in seconds. With it, you can:

  • Create unlimited mock REST APIs locally with no account required.
  • Simulate errors, latency, and complex API behaviors.
  • Speed up both frontend and backend development by removing dependencies.
  • Share your mock environments with your team (via JSON files or the optional Mockoon Cloud).

It’s available as a cross-platform desktop app, a CLI tool, and a Docker image.

Installation

Mockoon is available for macOS, Windows, and Linux. You can download the application directly from the official website.

macOS (via Homebrew)

If you’re on a Mac, the fastest way to install the desktop app is with Homebrew:

brew install --cask mockoon

CLI (Optional)

For automation, scripting, or use in CI/CD pipelines, you can install the CLI tool globally via npm:

npm install -g @mockoon/cli

Adding a Mock API

  1. Open the Mockoon app and click “New local environment”.

  2. Select a local folder to save the environment json file.

  3. Add a new route by clicking the + icon. Set the path (e.g., /users).

    Mockoon dashboard showing the main interface with the New Route button highlighted

  4. Configure the response in the right-hand panel:

    • Set the HTTP status code (e.g., 200 OK).
    • Switch to the “Body” tab and paste your JSON response.
    • Optionally, add headers in the “Headers” tab.

    Response configuration panel displaying the Body tab with sample JSON response

  5. Start the mock server by clicking the green ▶️ Start button at the top.

  6. That’s it! Test your new endpoint in your browser or with a tool like curl. By default, the server runs on port 3000, but this is easily configurable on the Settings tab.

# Your API is now live!
curl http://localhost:3000/users

Powerful Advanced Features

Mockoon is simple to start with but packed with advanced features for realistic simulations:

  • Dynamic Templating: Use Handlebars syntax to generate dynamic and realistic data. Perfect for creating non-static responses.

    {
  "id": "{{uuid}}",
  "name": "{{faker 'name.findName'}}",
  "email": "{{faker 'internet.email'}}",
  "createdAt": "{{now 'iso'}}"
}

  • Simulated Latency: Add a delay to responses (e.g., 2000ms) to test how your service’s timeout configurations and retry mechanisms behave.

  • Rule-Based Responses: Serve different responses based on request headers, query parameters, or body content. For example, you can return a 401 Unauthorized error if an Authorization header is missing, or a 200 OK if it’s present.

  • Proxy Mode: Forward requests that don’t match any of your mock routes to a real API. This is great for partially mocking a service while letting other calls pass through.

  • Import/Export: Quickly bootstrap an environment by importing an OpenAPI/Swagger specification.

Conclusion

Mockoon is an essential tool for modern development workflows. Whether you’re building a frontend without waiting for backend APIs, testing edge cases and error scenarios, or working offline, Mockoon provides a fast and flexible solution. Its rich feature set—from dynamic templating to rule-based responses—makes it suitable for both simple prototyping and complex integration testing.

Give it a try and see how much faster your development cycle becomes!