Mockttp
Mockttp is an open-source JavaScript library for intercepting, transforming, and testing HTTP requests and responses.
What Mockttp is
Mockttp is an open-source JavaScript library for intercepting, transforming, and testing HTTP requests and responses. It supports HTTP integration tests in Node.js and browsers, with transparent proxying and HTTPS, and can also be used to build custom proxies that capture, inspect, or rewrite traffic. Its mocking tools stub responses, verify requests, generate self-signed certificates for HTTPS, and mock traffic inside or outside the process. Parallel tests can use automatically configured ports, mock URLs, and proxy settings. Mockttp works with promise-capable testing tools and HTTP clients; Mocha, Chai, and Superagent appear in an example but are optional. Browser tests need an admin server started outside the browser. The library is free and available for Linux, macOS, Windows, web, and self-hosted use. The setup guide cautions against trusting a test certificate authority system-wide or sharing its private key, because either could enable impersonation of secure connections.
Good
- Free, open-source JavaScript library.
- Supports HTTP and HTTPS integration tests.
- Can mock traffic inside or outside its process.
- Automatically configures ports and proxy settings for parallel tests.
Watch out
- Browser tests require an external admin server.
- Trusting or sharing a test CA key creates security risks.
Who it suits
Mockttp suits JavaScript developers who need HTTP mocking, proxying, or integration tests across Node.js and browsers. It also fits teams running parallel tests or building custom traffic-inspection proxies.
Verdict
Mockttp combines HTTP testing and proxy capabilities in a free JavaScript library. Browser testing requires separate server setup, and its test certificates need careful handling.
Plans and prices
From Mockttp's own pricing page, checked 4 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| Hobbyist | Free | basic traffic viewing and rewriting · manual breakpoints · built-in HTTP client · Free |
| Professional | — | automated mocking and rewriting · import/export · advanced debugging and configuration · per month |
| Team | — | team licensing · centralized billing · team workspaces coming soon · additional options on request · per user, per month |
The facts
Each one read from Mockttp's own pages, with the date it was checked.
Where it runs
- Browser setup
- Browser tests require an admin server started outside the browser because browsers cannot start an HTTP server or proxy themselves.checked 4 Oct 2026
- Desktop platforms
- HTTP Toolkit provides installation packages for Windows, Mac, and Linux.checked 4 Oct 2026
What it does
- Commercial product distinction
- HTTP Toolkit lists automated HTTP mocking and rewriting among Professional plan features, while Mockttp itself is published as a JavaScript library in a public GitHub repository.checked 4 Oct 2026
- HTTPS certificate caution
- The setup guide warns against trusting a test CA system-wide or sharing its private key, because doing so could let an attacker impersonate secure connections.checked 4 Oct 2026
- HTTP Toolkit privacy
- HTTP Toolkit says HTTP request and response contents are never collected and are stored only locally on the user’s machine.checked 4 Oct 2026
- Integrations
- The README example uses Mocha, Chai, and Superagent, while noting that these tools are optional and Mockttp can work with other promise-capable testing tools and HTTP clients.checked 4 Oct 2026
- Mocking features
- The library can stub responses, verify requests, mock HTTPS with generated self-signed certificates, and mock traffic inside or outside its process.checked 4 Oct 2026
- Parallel testing
- Mockttp supports parallel mocking with automatically configured ports, mock URLs, and proxy settings.checked 4 Oct 2026
- Proxy use
- Mockttp can be used to build custom HTTP proxies that capture, inspect, or rewrite traffic.checked 4 Oct 2026
- Security support
- The latest published Mockttp version is actively supported, and the preceding major version receives security fixes for six months after the next major release.checked 4 Oct 2026
- Testing use
- Mockttp supports HTTP integration tests that can run in Node.js and browsers, including transparent proxying and HTTPS.checked 4 Oct 2026
- Vulnerability reporting
- Mockttp vulnerabilities can be reported through GitHub’s private security reporting channels, and confirmed vulnerabilities are to be fixed and published as advisories within 90 days.checked 4 Oct 2026
- What Mockttp does
- Mockttp intercepts, transforms, or tests HTTP requests and responses in JavaScript.checked 4 Oct 2026
The company
- Maker and location
- The HTTP Toolkit privacy policy identifies Toolshed Labs SLU as the operator and gives its address in Barcelona, Spain.checked 4 Oct 2026
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