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Mockttp

github.com

Free plan WebWindowsmacOSLinuxSelf-hosted
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Spec score 7.8 #12 of 26 in API Mocking Tools

What it is

Mockttp is a free, open-source JavaScript library for intercepting, transforming, or testing HTTP requests and responses. It supports integration tests in Node.js and browsers, including transparent proxying and HTTPS. Its tools can stub responses, verify requests, generate self-signed certificates for HTTPS mocking, and mock traffic inside or outside the process. It can also serve as the basis for custom proxies that capture, inspect, or rewrite traffic. For parallel tests, Mockttp can automatically configure ports, mock URLs, and proxy settings. It works with promise-capable testing tools and HTTP clients; Mocha, Chai, and Superagent appear in an example but are optional. Browser tests require an admin server running outside the browser. The setup guide warns against trusting a test certificate authority system-wide or sharing its private key, because either could allow an attacker to impersonate secure connections. Mockttp supports Linux, macOS, Windows, web, and self-hosted use.

Spec sheet

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.Read 4 Oct 2026 · github.com
Browser setup
Browser tests require an admin server started outside the browser because browsers cannot start an HTTP server or proxy themselves.Read 4 Oct 2026 · github.com
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.Read 4 Oct 2026 · httptoolkit.com
Desktop platforms
HTTP Toolkit provides installation packages for Windows, Mac, and Linux.Read 4 Oct 2026 · httptoolkit.com
HTTP Toolkit privacy
HTTP Toolkit says HTTP request and response contents are never collected and are stored only locally on the user’s machine.Read 4 Oct 2026 · httptoolkit.com
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.Read 4 Oct 2026 · github.com
Maker and location
The HTTP Toolkit privacy policy identifies Toolshed Labs SLU as the operator and gives its address in Barcelona, Spain.Read 4 Oct 2026 · httptoolkit.com
Mocking features
The library can stub responses, verify requests, mock HTTPS with generated self-signed certificates, and mock traffic inside or outside its process.Read 4 Oct 2026 · github.com
Parallel testing
Mockttp supports parallel mocking with automatically configured ports, mock URLs, and proxy settings.Read 4 Oct 2026 · github.com
Proxy use
Mockttp can be used to build custom HTTP proxies that capture, inspect, or rewrite traffic.Read 4 Oct 2026 · github.com
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.Read 4 Oct 2026 · github.com
Testing use
Mockttp supports HTTP integration tests that can run in Node.js and browsers, including transparent proxying and HTTPS.Read 4 Oct 2026 · github.com
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.Read 4 Oct 2026 · github.com
What Mockttp does
Mockttp intercepts, transforms, or tests HTTP requests and responses in JavaScript.Read 4 Oct 2026 · github.com

Plans and prices

Hobbyist Free Free basic traffic viewing and rewriting · manual breakpoints · built-in HTTP client Read 4 Oct 2026 · httptoolkit.com
Professional Price not published per month automated mocking and rewriting · import/export · advanced debugging and configuration Read 4 Oct 2026 · httptoolkit.com
Team Price not published per user, per month team licensing · centralized billing · team workspaces coming soon · additional options on request Read 4 Oct 2026 · httptoolkit.com

Every Mockttp plan and price →

Strong points and limits

Strong points

  • Tests HTTP requests and responses in Node.js and browsers
  • Supports transparent proxying and HTTPS
  • Automates port and proxy configuration for parallel tests
  • Free and open source

Limits

  • Browser tests require an external admin server
  • Test certificate authorities require careful handling

Who it suits

Mockttp suits JavaScript developers building HTTP integration tests or custom proxies. It can work with different promise-capable testing tools and HTTP clients.

Verdict

Mockttp provides request and response mocking, verification, and proxy capabilities for JavaScript projects. Browser tests need an external admin server, and the certificate guidance is important when configuring HTTPS mocking.

Where Specifiction places it

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