I started writing HTTP status code guides for my SaaS business: https://tryhexadecimal.com/guides/http/

A lot of guides on the Internets concerning HTTP status codes are regurgitations or outright ripoffs of RFCs (2616 or 7231). Or light on details.

I want(ed) to go one step further and explain when each code is appropriate (from the website operator's perspective), how to work around some of the errors (mostly for 4xx and 5xx), and some context around HTTP headers/methods.