Install w3c-markup-validator by entering the following commands in the terminal:
sudo apt update sudo apt install w3c-markup-validator
Description:
W3C Markup Validator
The W3C Markup Validator is a CGI script which lets you enter the URL of a web page which will be then checked against a validating SGML parser for conformance to official W3C recommendations. Pages can also be uploaded. . These are the same scripts that are available on the W3C web site, http://validator.w3.org/.
Homepage: https://validator.w3.org/about.html
Version: 1.3+dfsg-4
Section: universe/web