CardScopeFree check
Slack link preview checker
Checks the tags Slack reads to unfurl a link.
Uses the email from Checkout. If that address paid, we send the same key.
What Slack reads
From this fetch. Not Slack’s unfurl.
Slack preview
Slack reads og:title, og:description, and og:image first. A missing Open Graph tag can fall back to the matching Twitter tag.
theme-color may set the color of the bar beside the unfurl. Slack doesn’t document it, and the bar stays gray unless the value is a hex color. An oEmbed link is optional. Slack can still unfurl the page from Open Graph.
Slack may keep an older unfurl after the tags change. This check reads the live page. How Slack and Discord unfurl a URL