Weer is described as 'A HTTP protocol debugger with Chrome DevTools frontend interface' and is an app in the Development category. There are more than 10 alternatives to Weer for a variety of platforms, including Mac, Windows, Linux, iPhone and iPad. The best alternative is Fiddler, which is free. Other great apps like Weer are mitmproxy (Free, Open Source), Charles (Paid), OWASP Zed Attack Proxy (ZAP) (Free, Open Source) and HTTP Toolkit (Freemium, Open Source).
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.
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).
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.