Plumbtern: On-Page SEO Checker, published by Zydeno.

The extension stores data only in your browser (storage.local). Nothing is sent to Zydeno or anyone else. There are no analytics, no accounts and no network requests.

When you click the toolbar button or press the shortcut, Plumbtern reads the page in the active tab and shows the result in its popup. Stored on your device: your language and theme if you change them, and baselines only when you press Save as baseline (page address, date, title, description, canonical, robots, H1, hreflang, Open Graph and social card tags, JSON-LD types, language, counts of headings, images, links and words). You can delete baselines in the popup or in Settings, and removing the extension removes them.

Permissions:
activeTab: access to the open tab only after you click the button or press the shortcut.
scripting: runs the read-only check in that tab, and outlines an element when you ask to see it.
storage: keeps settings and baselines on this device.

Contact: support@zydeno.com