Someone above recommended devd, and it looks pretty nice. https://github.com/cortesi/devd

I personally like busybox httpd, because sometimes it already is there.

mini_httpd, merecat, [a-z]httpd (choose one), OpenBSD httpd is nice but not portable. Your OS likely has a a built-in web server. Hell, Microsoft shipped something called Personal Web Server with Windows 95/98 nearly 30 years ago.

Stop inventing new static web servers. Contribute patches to an existing project if you feel so inclined but this has been a solved problem for decades by very intelligent people who understand how the Internet works. We've gone full circle from bloated behemoths like Netscape, to serving from kernel mode (http.sys, Tux Web Server, etc.) and back again.