Mastodon does not run its own card service. When a user posts a link, the Mastodon server fetches the URL, parses the head, and uses og:image and og:title to build the link preview shown inline in the timeline. The format is roughly 1200x630, the same as the Open Graph standard. Sites that already have a clean og:image render correctly on Mastodon without any platform-specific work, and sites that rely on a stretched featured image render with the same crop problems they have on every other platform.

SleekPixel renders the og:image during the save lifecycle. The 1200x630 PNG carries the post title, author, and brand mark, written to the uploads directory and registered in the post head. When the URL gets shared on a Mastodon instance, the server fetches the head, finds the og:image, downloads it once, and shows the card in the timeline. Each instance caches independently, so widely shared links get fetched by dozens of instances over the first few days, and a real card means each fetch shows a real preview.

Because the work is OG-standard, the same render covers Bluesky, link previews in many Slack DMs and Discord embeds, and any other reader that respects og:image. The fediverse becomes a target without writing per-platform code.

The fediverse is a graph of independent servers that each fetch and cache previews on their own. A single popular post can trigger fetches from dozens of instances over a few days, and the preview each instance caches is what every user on that instance will see. A missing or broken og:image therefore caches as a broken preview across the entire reach of the post, and the broken state lasts as long as the cache does.

The cost of getting og:image right is paid once at save time. The cost of getting it wrong is paid by every instance and every user who never sees a real card. SleekPixel removes the cost of getting it right by rendering the card from a template at save time.

Branding refreshes propagate by re-rendering the archive, instances refresh their caches on the next fetch, and the long tail of fediverse shares carries the current brand instead of an old broken preview. The work that used to live in a designer-and-editor handoff moves into the post save lifecycle, and the fediverse stops being a special case.