What is the use of HTML in ethical hacking?

To become a successful web hacker you should know how to code in HTML because the only code the user or a hacker sees first on the page is HTML and in that code contain links to the server is associated. The links which hacker found can be used to gain access to the server (if a hacker found any vulnerability).

The links are very helpful to predict the file hierarchy in the server side and the hacker can find some files which are associated with database server or files containing some important stuff.

These things only understood by the peoples who are writing html with some server side programming knowledge so if you want to become a good web hacker you should learn HTML with some server side programming language.