The best alternative to Fiddler is HTTP Toolkit, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to Fiddler and seven of them are so hopefully you can find a suitable replacement. Other interesting alternatives to Fiddler are NetworkMiner, Advanced REST Client, PolarProxy and HttpFox.
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.
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.
API testing tool. Which allows web developers to create and test custom HTTP requests.
PolarProxy is a transparent SSL/TLS proxy. PolarProxy decrypts and re-encrypts TLS traffic, while also saving the decrypted traffic in a PCAP file that can be loaded into Wireshark or an intrusion detection system (IDS).
HttpFox monitors and analyzes all incoming and outgoing HTTP traffic between the browser and the web servers.
Speedrank monitors the performance of your website in the background. It displays Lighthouse reports over time and delivers recommendations for improvement. Speedrank is a paid product with 14-day-trial.
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Fiddler is a Proxy tool used to intercept and examine HTTP requests not to create an test HTTP requests.