Toolkit for implementing a validator?

Question

css

Greetings.
There is a task to implement an HTML/CSS validator in JS.
I would like to hear recommendations on what features of JavaScript to consider when working, and maybe someone will advise specific tools and tools (any JS libraries, for example).
Thank you in advance.

Answer 1

validator.w3.org/docs/api jigsaw.w3.org/css-validator/api.html