HTTP Toolkit - Beautiful, cross-platform & open-source tools to debug, test & build with HTTP(S). One-click setup for browsers, servers, Android, CLI tools, scripts and more.
PreFlight - Preflight is an Automated Web Testing tool. Allows everyone to automate Web UI tests.
Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
HTTP Status Dogs - Hypertext Transfer Protocol Response status codes, and dogs
DebugBear - Track site speed and Core Web Vitals
HTTP Status Cats - Cats for every HTTP status code, by ex-Google.