HTML Validator is a free online developer tool to validate HTML code against the W3C standards as known as HTML linter instantly. Supports partial HTML code validation.
You can either browse an HTML file, fetch HTML code from a URL, or paste HTML code manually, and then click the validate button. The results will be displayed accordingly when the process is done.
Basically, there are two types of result messages:
Warning - A suggestion to fix your HTML code. For instance, an HTML attribute that can be omitted.
Error - An error in your HTML code that's against the W3C standards. You're encouraged to fix it.
Each message comes with a line number and excerpt code indicating where a warning or an error is located.
Optionally, you can partially validate HTML code by enabling the
fragment option so that the HTML code will be treated as part of an HTML document instead of a full one.