I only recently learned that HTTP methods are case-sensitive. In order to save myself from future debugging headaches, I decided to do a quick search to see what else is case-sensitive.

This is what the RFC says. Real applications may treat things differently!

Summary

Case-sensitive:

• HTTP version
• Method
• URI path, query, fragment
• Header field values
• Body

Case-insensitive:

• URI scheme
• URI host
• Header field name
• Transfer-coding header value
• Connection header value