Hi z64 ,
giving help here, If you need to.
Surely https://linux.die.net/man/ is a good practical choice for starting; for the future, the problems I see are:
- is stagnating since few years
- are only a bunch of good-will US friends
Another choice that could solve these two problems are Debian manpages: https://manpages.debian.org/
If you'll do the POST on the form, the urls doesn't seems to obey to your necessary condition: a simple querystring parameter.
But look closely to the explanation: to search the man page for "top" command, you could simply load https://manpages.debian.org/top , and the engine will fill in the other parameters (suite, binarypackage, etc)
Surely Debian is only a distribution, but surely a very old, extended and stable one...and I think that these pages will be up-to-date, reachable, mantained.
If you don't like this idea, please tell me and I'll go searching again.