| Image size | 1200x675px |
| Aspect ratio | 1.78:1 |
| Max file size | 5 MB |
| Formats | image/jpeg, image/png, image/webp, image/gif |
| User-Agent | Mastodon/4.3.0 (http.rb/5.2.0; +https://mastodon.social/) |
Mastodon generates preview cards when a URL is shared in a status, pulling data from Open Graph meta tags and oEmbed endpoints. Unlike centralized platforms, every Mastodon instance fetches and caches preview data independently, so your link can look different across the fediverse.
This guide covers how Mastodon’s per-instance crawling works, which tags it reads, image sizing rules, cache behavior, and the most common issues that prevent preview cards from appearing.
Per-instance fetching, user agents, and why the fediverse is different
Which Open Graph, Twitter, and fediverse tags Mastodon actually reads
How Mastodon processes, resizes, and displays preview card images
How Mastodon caches preview cards and why there's no universal refresh
Troubleshooting the most frequent Mastodon preview card problems
Enter your site's URL to see how it looks on Mastodon.