Tool, not site. However, let me try to add a little value: if, like me, you didn’t know the IETF’s site offered a tool for web-friendly RFC viewing, check out the full (maybe?) list of their tools. Some of the links don’t work or are insecure, but there are some neat scripts available, too[0].
Linking urls and cross-referenced articles is why I prefer sites like man7[1], for online command reference.
[0] https://tools.ietf.org/
[1] https://www.man7.org/linux/man-pages/index.html