Hugo web server - localhost vs

Using hugo to render some webpages and trying to use local server: hugo server -D

documentation states connect to: http://localhost:1313 - does not work. When I eventually tried 127.0.01:1313 out of frustration - it does work! Has nothing to do with FireJail or firewall.

Using other webtools and local development servers I have not until now had a problem connecting to local ports.

So what exactly is going on here ? is localhost or loopback. they are all the same but is the actual “address”