What are the solutions for completing HTML tasks online?

Question

HTML

On the basis of what services or libraries (including English-language and paid ones) can you make something like htmlacademy where there is a part of the code, the user has the task to supplement it. He writes his code in the window, the system checks whether he says so or not.

Answer 1

https://www.npmjs.com/package/w3c-validate
https://www.npmjs.com/package/node-w3c-validator
https://www.npmjs.com/package/html-validator
https:/ /www.npmjs.com/package/html-validate
https://www.npmjs.com/package/html5-validator

Answer 2

What can you check in HTML? HTML is like an essay - you can write it in different ways, but get the same result.