OG Tag Preview

Where previews come from

When you paste a link into Slack, iMessage, X, or Facebook, the platform fetches the page once and reads its Open Graph tags (`og:title`, `og:description`, `og:image`) — a protocol originally from Facebook, now universal (ogp.me). No OG tags means the platform guesses, usually badly.

Rules that prevent broken previews

• `og:image` must be an absolute URL (https://...), at least 1200×630 for large cards, under ~5MB.
• The image URL must be publicly reachable — no login walls, no localhost.
• Platforms cache previews aggressively. After fixing tags, force a re-scrape (Facebook Sharing Debugger, LinkedIn Post Inspector) — just re-pasting the link shows the stale cache.
• X reads Twitter Card tags first (`twitter:card`), falling back to OG. `summary_large_image` gives the big preview.

Debugging order

Preview broken? Check in this order: tags present in server HTML (not injected by JS) → absolute image URL → image size → platform cache.