HTML Validator

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Validating web pageThis extension helps to validate a web-page using a validator created by Philip Walton.

This will be a useful tool when it comes to checking pages create follow HTML standards. This is especially useful for accessibility(ARIA attributes) and cleaning up un-used markup.

Usage : Open the developer tools, goto Console. Click on the extension on the browser. All the errors/warning will be shown on the console.

Reference:
Blog Link : http://philipwalton.com/articles/introducing-html-inspectorlity
Validator Source Code : https://cdnjs.cloudflare.com/ajax/libs/html-inspector/0.8.1/html-inspector.js