Open Graph and social cards

Facebook introduced the Open Graph protocol in 2010, and nearly every app that builds link previews now reads it. The core tags are og:title, og:description, og:image, og:url and og:type, written as meta tags in the page's head. X reads its own twitter:card tags and falls back to Open Graph for the rest. An image of 1200 by 630 pixels displays well on most platforms.

Previews are fetched once and cached, so an updated image may not appear until the cache is refreshed with tools such as Facebook's Sharing Debugger or LinkedIn's Post Inspector. Image URLs must be absolute and publicly reachable. Frameworks such as Next.js can generate a card image for every page automatically.