What is an Open Graph checker?
An Open Graph checker reads the hidden tags in a page’s HTML that social apps use to build a link preview: the title, short description and picture you see when someone shares the address. Open Graph was created by Facebook and is now read by LinkedIn, WhatsApp, Slack, Discord, Telegram and others; X adds its own Twitter Card tags. This checker shows the tags, draws the preview, and tells you what is missing before you share.
The tags every page should have
| Tag | Example |
|---|---|
| og:title | <meta property="og:title" content="Radius Map"> |
| og:description | One or two sentences, under about 200 characters |
| og:image | Full https:// address of a 1200 × 630 image |
| og:image:alt | A short description of the image, read aloud by screen readers |
| og:url | The canonical address of the page |
| og:type | website for most pages, article for posts |
| twitter:card | summary_large_image |
What the checker tests
- Fix:
og:titleorog:imageis missing, or the image address does not load. - Tip:
og:description,og:urlortwitter:cardis missing; the image is smaller than 1200 × 630; orog:titleis longer than 90 characters and will be cut off. - OK: the image loads and is at least 1200 pixels wide.
The image is measured by loading it in your browser, the same way a social app would. The page itself is fetched once by our server, so a page behind a login shows its logged-out tags, which is what social apps see too.
How each app builds the preview
| App | Reads | Notes |
|---|---|---|
| og: tags | Caches the preview; refresh it in the Sharing Debugger | |
| og: tags | Caches for about a week; refresh it in Post Inspector | |
| og: tags | Often shows a small square thumbnail; keep text in the centre of the image | |
| X (Twitter) | twitter: tags, then og: | Needs twitter:card = summary_large_image for the big picture |
| Slack, Discord, Telegram | og: and twitter: tags | Show the site name from og:site_name when it is set |
Why is my link preview wrong or not showing?
- An old preview: the app cached it before your fix. Use Facebook’s Sharing Debugger or LinkedIn’s Post Inspector; on WhatsApp, a slightly changed address (such as adding
?v=2) is fetched fresh. - Relative image paths such as
/img/share.png: some platforms need the full address. - Tags added by JavaScript: share crawlers read only the original HTML, so tags must be in the page source.
- The site blocks bots: a firewall that challenges unknown visitors also blocks the apps’ preview crawlers, so no card appears.
- One image for every page: works, but a page-specific image gets more clicks.
Check the raw HTML with View Page Source, or every link on the page with the link analyzer. To open a list of your pages in tabs and review them one after another, use the multiple URL opener.