For the complete documentation index, see llms.txt. Markdown variants are available by appending .md to any URL or sending an Accept: text/markdown header. An agent skill is available at /.well-known/agent-skills/site-skill.md.
Paste a URL and see the link card Mastodon will build from it.
Mastodon expands a wide preview image above the text. Under it, the card shows the provider or hostname, a bold title, and one clipped description line. Images wider than they are tall use the expanded layout; small or square images move into a compact thumbnail row.
Use a 1.91:1 image such as 1200×630 and keep essential text away from the edges. Mastodon instances cache preview cards, so an old share may keep the earlier image after you update the page.
Each Mastodon server fetches links for its own users. A page that blocks the instance's bot, requires a login, or returns incomplete metadata can appear as a bare link on one server even when another server already has a cached card.
Set og:title, og:description, og:image, and og:url. Add og:site_name when you want a recognizable provider name above the title. The crawler row above shows whether Mastodon could fetch both the page and its image.