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Every platform builds its preview from a different set of tags, with a different fallback order. A page can look perfect on X and broken on LinkedIn, and the tags themselves will not tell you which. previews resolves all eight for you.

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The eight

Each preview carries its own basis string stating these rules, so the response explains itself without this table.
Where a platform’s behaviour is undocumented, the resolver is deliberately conservative — it assumes no twitter:* fallback rather than guessing one. Predicting a preview that does not appear is a worse failure than predicting a plainer one that does.

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What each one returns

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source is the field to read

Two pages can produce an identical preview for entirely different reasons. source tells you which tag did the work:
versus
The second page has no Open Graph tags at all. It still previews — because platforms fall back — but you are getting whatever the fallback produces rather than what you chose. That distinction is invisible in title alone.

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approximate

Every preview is approximate: true, and the field exists to say so rather than to distinguish good pages from bad ones. No platform publishes its exact rendering rules, and real output depends on things invisible from the HTML: A/B tests, personalisation, the platform’s own crawl cache, and layout rules that change with image aspect ratio. Google is the extreme case — search results are generated rather than rendered, and it may rewrite your title entirely if something else matches the query better.
approximate: true is not a warning about your page. It is us declining to overstate how precisely anyone can predict a third party’s renderer.

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Why Google ignores Open Graph

The single most common misunderstanding this endpoint clears up. Google builds search results from <title> and meta description. It does not read og:title or og:description. A page with immaculate Open Graph tags and no meta description will preview beautifully on Facebook and show Google’s own guess at a snippet. That is why missing_description is a warning even on a page with a full set of og: tags.

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Platforms cache aggressively

A preview here reflects your page now. What a platform shows reflects whenever it last crawled you, which can be days. After fixing tags, most platforms need to be told to look again:
  • Facebook and Instagram — the Sharing Debugger, “Scrape Again”
  • LinkedIn — the Post Inspector
  • X — re-share; the card is refetched on a schedule
  • Slack, Discord, WhatsApp, Telegram — cache by URL for hours; a ?v=2 query parameter forces a fresh fetch
If a preview here looks right but the platform still shows the old one, the tags are fixed and the platform is stale. Purge its cache rather than editing further.