Free Web Debuggers

mitmproxy is an SSL-capable man-in-the-middle proxy for HTTP. It provides a console interface that allows traffic flows to be inspected and edited on the fly. It also features mitmdump, a commandline tool that provides a tcpdump-like interface for saving, viewing and...

Fiddler is a Web Debugging Proxy which logs all HTTP(S) traffic between your computer and the Internet. Fiddler allows you to inspect all HTTP(S) traffic, set breakpoints, and "fiddle" with incoming or outgoing data.

The Google Chrome Developer Tools provide an integrated environment for debugging, optimizing, and understanding a web application, or website, running in Google Chrome. The developer tools are developed partly through the WebKit open source project, where the tools are called...

HTTP Toolkit is a beautiful, cross-platform & open-source HTTP(S) debugging proxy, analyzer & client, with built-in support for modern tools and automatic interception for clients from Docker to Android to iOS.

Requestly is a lightweight proxy available as a browser extension & desktop app to intercept & modify network requests. Using Requestly you can Modify Headers, Redirect Url, Mock API response, Delay/Throttle requests, etc.

CodeTracer is a user-friendly time-traveling debugger designed to support a wide range of programming languages.

Examine, edit, and debug HTML, CSS, and JavaScript on the desktop and on mobile.

AI-native platform for intelligent, automated testing of web, mobile, and enterprise apps at scale with real device, browser, and environment support.

MultiGlancer is a minimalist and open-source tool I've developed to streamline the web development process. It allows developers to view their site on multiple web sizes simultaneously on a single screen. Born out of necessity while perfecting my landing page for ArcanePad.

The Web Developer extension adds various web developer tools to a browser. The extension is available for Chrome, Edge, Firefox, and Opera, and will run on any platform that these browsers support including Windows, macOS and Linux.

The Zed Attack Proxy (ZAP) is an easy to use integrated penetration testing tool for finding vulnerabilities in web applications.

Develop responsive web apps 5x faster! A must-have DevTool for all Front-End developers that will make your job easier.

Performs real-time mobile and tablet website debugging, offers 50+ device profiles, supports custom resolutions, and features built-in Dev Tools for simultaneous responsive testing.

Sorry Cypress is an open-source platform that serves as an alternative to the Cypress Cloud

James is a HTTP Proxy and Monitor that enables developers to view and intercept requests made from the browser. It is an open-source alternative to the popular developer tool Charles.

HttpFox monitors and analyzes all incoming and outgoing HTTP traffic between the browser and the web servers.

The goal of this project is to adds information about the HTTP headers in three ways:

HTTP Headers allows you to quickly see the HTTP header information for the current URL.

Domsignal is an all-in-one platform dedicated to empowering developers, SEO experts, sysadmins, and security researchers in their quest for website excellence. We provide a comprehensive suite of tools to help you analyze and optimize your website's performance, security...

ReqRes is an open-source, high-performance, modern native web debugging proxy for macOS. It lets you capture, inspect, modify, and intercept HTTP(S) traffic in real time.

Blisk is a browser for web developers, QA engineers, and web designers with built-in mobiles, tablets, laptops, and desktops. It provides teams and freelancers with a workspace to develop and test modern web applications twice faster.

Lonkero is a high-performance web vulnerability scanner built in Rust for penetration testers and bug bounty hunters who are tired of slow, bloated tools that generate hundreds of false positives.

Omnibug is a plugin for the Google Chrome and Mozilla Firefox browsers to ease developing and debugging web metrics implementations. Each outgoing request (sent by the browser) is checked for a pattern; if a match occurs, the URL is displayed and decoded to show the details of...