The first full featured, in-browser HTML5 validator for Chrome

A HTML5 validation plugin for Google Chrome

Based on HTML Tidy for HTML5 as can be found here:

Compiled to JavaScript using Emscripten as can be found here:

 Key features:

  • Full error checking by TIDY Library
  • No need to make calls to external services
  • No need to install extra software
  • See directly wether a page is valid HTML (5) or not, in a non obtrusive way
  • Use your original network traffic to analyse the source code: validate the HTML you received from the server.

The Github repository can be found here: Please report issues and/or give feedback there.


  • Closure-compile tidy_cli.js with Virtual Filesystem options
  • Add a source-view tab with highlighting

The Chrome plugin can be installed here: