Common issues

The handful of things that trip people up, and the fix for each.

The tooltip does not appear

Make sure the extension is active (click the WhatTheCSS toolbar icon; the scanning bar should be visible). On file:// pages, serve the file through a local web server, Chrome treats every file:// URL as a separate origin. Activation is per-tab and does not survive a reload or navigation, so on a fresh page click the icon again.

Edits do not stick

Live edits apply to the running page and are cleared on reload, by design. They are for trying values, not persisting them. To keep a value, copy the CSS and put it in your source.

License will not activate

Confirm the key is entered exactly as in your purchase email (a 36-character UUID like xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx). If all three device slots are used, free one from license management. Pro state is cached for 30 days offline, so a brief network failure will not lock you out.

Framework variables show up

WhatTheCSS filters --tw-*, --chakra-*, and --mui-* noise automatically. If a framework prefix still leaks through, it is one we do not yet filter, email support@whatthecss.dev with the prefix and we will add it.

Shadow DOM and cross-origin

Open Shadow DOM components are inspected normally. For cross-origin stylesheets the extension falls back to computed style and shows a banner explaining the downgrade. Cross-frame (iframe) inspection is intentionally off.