Not to rain on your parade with nicely formatted code like hardly any shell projects do, but what I would have expected for such a tool that I just want to use:
Only gave it a quick look and saw the other comment asking for dependencies. if there are some, why not list them in the README.
I'm really not against installers, but falls under the "small handy tool" category and not "I will spend time automating the install, either it works or it doesn't"
I'm really sorry to the OP if I seemed annoyed, but I was merely stating my first impression.
I'm not a big fan of shell scripts for complicated tasks, but their main benefit is exactly "one file, runs everywhere, it just works" - if you take away all three of those I question if it's the right choice being a shell script. For tools of this scope I really like go. stuff everything together as a static binary and you're good to go.
Why are you using a URL in place of a domain name, in the invocation example? Seems confusing. I would expect to see just a domain name there. Although I wouldn't complain if it works with both a domain and a full URL, automatically stripping off the parts it doesn't need. Also seeing http:// instead of https:// is starting to feel strange these days, but I do realize both are still used and your tool works with both as it should.
Very nice readme! And nice to see it has a man page. I would leave out the "It's simple:" line because that tends to make less confident people (like new people just learning) blame themselves if they have problems, and then instead of giving you feedback they'll give up and move on.
I suggest a convenient way to set cookie or auth headers. A lot of endpoints are behind authentication. The --req-headers flag is feasible, but there should be a shortcut flag just for authentication headers. Maybe --cookie and --auth ?
Here is a similar tool all contained in one shell script that only depends on openssl. [1] Albeit, a bit more verbose and doesn't have that nice one page output.
wget https://github/.../releases/.../stable/htrace.sh
Only gave it a quick look and saw the other comment asking for dependencies. if there are some, why not list them in the README.
I'm really not against installers, but falls under the "small handy tool" category and not "I will spend time automating the install, either it works or it doesn't"