The first impression, checked everywhere at once.

No — every preview is a simulation, rebuilt in HTML and CSS from the tags your page serves and the rules each platform follows (which tags it reads, when it switches between a large image and a thumbnail, where it cuts text). The rules come from platform docs and, where possible, the apps' own source code. Apps change their designs often, so treat a preview as a very good estimate and confirm launch-critical links in the real app.

Only the URL you submit. We request it once with our own user agent, then once with each platform's published crawler user agent to spot sites that serve bots something different. We read the <head>, then download the og:image and the icons it declares. We don't follow links, crawl other pages, run JavaScript or log in anywhere.

robots.txt governs automated crawling. We fetch a single page because a person asked us to, the same way Slack, iMessage or WhatsApp fetch a link the moment someone pastes it — and those platforms don't consult robots.txt for previews either. If your preview is broken for a platform, we'd rather show you than hide it.

Each check is saved as a snapshot — the tags we found plus copies of the preview image and icons — so its permalink keeps rendering even after the site changes. Snapshots live at unguessable, unlisted URLs, are never indexed, and are deleted after 90 days. The browser that ran a check can delete its snapshot immediately. Your list of recent checks never leaves your browser.

Some bot-protection services block unfamiliar crawlers (sometimes including smaller platforms' real ones — worth knowing). Use “Paste HTML”: paste your page's <head> and we'll render every preview without fetching the page itself. It also works for localhost and staging sites behind a login.

Platforms cache previews — Slack and Discord for about 30 minutes, X for about a week, Facebook and LinkedIn until you ask them to re-scrape. Each tile has a ↻ refresh note with the platform's tool or workaround (usually: share the URL with a new query string like ?v=2).

No. Platform names are used only to say which app a preview simulates. We don't use their logos.