Comments within HTML code are added using the following syntax.
<!-- This is a HTML comment -->
GET, PUT, e.t.c
The common command send when you type a URL into your browser is GET.
You can use the program curl on Linux-systems to send different commands to URLs.
$ curl -i -X GET http://my.url
Or you can use a web-based app such as the Simple REST Client.
Apiary (http://apiary.io/) is a useful tool for designing web-based APIs (APIs using HTML requests). It allows instant API mock creation with automatic documentation and testing. It is free for single, non-commercial users (aka hackers).