Fiddler is described as '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' and is a well-known app in the Development category. There are more than 25 alternatives to Fiddler for a variety of platforms, including Windows, Mac, Linux, Online / Web-based and Google Chrome. The best alternative is Wireshark, which is both free and Open Source. Other great apps like Fiddler are Charles (Paid), mitmproxy (Free, Open Source), OWASP Zed Attack Proxy (ZAP) (Free, Open Source) and Burp Suite (Freemium).
Wireshark is the world's foremost network protocol analyzer. It lets you capture and interactively browse the traffic running on a computer network. It is the de facto (and often de jure) standard across many industries and educational institutions.
Wireshark vs Fiddler opinions
pros, cons and recent comments
Wireshark is a packet analyzer, not an alternative to debugging proxy like Fiddler or MITM are.
Charles is an HTTP proxy / HTTP monitor / Reverse Proxy that enables a developer to view all of the HTTP and SSL / HTTPS traffic between their machine and the Internet. This includes requests, responses and the HTTP headers (which contain the cookies and caching information).
Charles vs Fiddler opinions
Almost everyone thinks Charles is a great alternative to Fiddler.
NetworkMiner is a Network Forensic Analysis Tool (NFAT) for Windows. NetworkMiner can parse PCAP files and regenerate/reassemble transmitted files and certificates from PCAP files with HTTP, FTP, SMB, SMB2, TFTP and several other protocols.