/tools/og-preview takes a URL and shows three side-by-side visual mocks of how it will appear when shared:

• Twitter / X — summary or summary_large_image depending on twitter:card.
• LinkedIn — image on top, title + hostname in the grey caption bar.
• Slack — site name + favicon, blue title, description, then the inline image.

A warnings panel calls out the common mistakes: missing og:image (links look bare), title > 70 chars (Twitter truncates), description > 200 chars, missing twitter:card (Twitter falls back to small image), and the always-painful "you forgot to add OG tags entirely".

Fetches the page server-side, parses meta + link tags, resolves the favicon, and renders everything in your browser — nothing is uploaded.