Layout Lens collects no data.

It transmits nothing to any server. It has no analytics, no telemetry, no crash reporting, no account, and makes no network requests of any kind.

What it stores: one true/false flag per browser tab recording whether the inspector is switched on. It is held in session storage, which exists only in memory, is never written to disk, and is cleared when you close the browser. Nothing else is stored.

What it reads: while the inspector is active, the position, size and computed CSS of the element under your cursor, to draw the overlay. Those values stay in the page, are replaced on the next frame, and are never saved or sent anywhere.

Pressing c copies the current measurement to your clipboard. That is the only thing the extension writes outside its own overlay, and only on that keypress.

Permissions: activeTab, granted only when you press the extension's shortcut, used to message the content script in that tab. storage, used only for the session flag above. The content script runs on all sites because it has to be present when you press the shortcut; until then it registers a single extension-message listener and does nothing else.