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CSS Diagnostics

Highlight potentially invalid or erroneous HTML markup.

An extension for Google's Chrome browser which highlights potentially invalid and erroneous HTML markup.

This extension uses a fork of the Holmes stylesheet.

Installing from the Web Store

On Google Chrome

Visit Google Chrome's webstore

Click the Add to Chrome button.

On Mozilla Firefox

Visit Firefox add-ons website

Click on the + Add to Firefox button.

Installing from source

  1. Clone the repository: git clone
  2. Navigate to chrome://extensions and enable Developer Mode.
  3. Choose "Load unpacked extension"
  4. In the dialog, open the directory you just cloned.


Just click on the extension icon to turn on/off the diagnostics stylesheet.

You will see warnings in yellow rectangles and errors in red rectangles.

An explanation of the warning/error is given when you mouseover it.

Don't hesitate to file an issue if you find something wrong or would like help.


Pull requests are welcome as long as they don't break the original idea of the extension.