The best open source alternative to Fiddler is mitmproxy. If that doesn't suit you, our users have ranked more than 50 alternatives to Fiddler and 17 is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Fiddler are HTTP Toolkit, Zed Attack Proxy (ZAP), NetworkMiner and Requestly.
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...
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.
The Zed Attack Proxy (ZAP) is an easy to use integrated penetration testing tool for finding vulnerabilities in web applications.
NetworkMiner is a Network Forensic Analysis Tool (NFAT) for Windows. NetworkMiner can extract transmitted files and certificates from PCAP files containing HTTP, FTP, SMB, SMB2, TFTP and several other protocols.
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.
API testing tool. Which allows web developers to create and test custom HTTP requests.
Stoplight is an API Design, Development, and Documentation platform that enables consistency, reusability, and quality, all with an easy, enjoyable developer experience.
ArdorQuery is a cross-platform tool for performing any HTTP(S) endpoints like REST API, HTML, Images, GraphQL, OData etc.
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.
If you're debugging on a remote machine with a large pcap and no desire to scp it back to your desktop, termshark can help!
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mitmproxy is able to edit response data