Technical
Twitter Card
Also called X Card.
Twitter Card is a set of `<meta name='twitter:...'>` tags that control the title, description, and image of a link preview on X, formerly Twitter.
How it is measured
View source for `twitter:card` (`summary` or `summary_large_image`), `twitter:title`, `twitter:description`, and `twitter:image`. Large-image cards want roughly a 2:1 ratio and under 5 MB. X's crawler is `Twitterbot`, so look for it in the log and make sure robots.txt lets it in.
When a card tag is missing, X falls back to the Open Graph equivalent. Test by pasting the URL into a draft post and looking at the preview.
Worked example
A podcast site has `og:image` set but no `twitter:card`, so its links show as small square thumbnails. Adding a `summary_large_image` card tag swaps in a wide image on the next fetch.
Another page's preview stays stale after a title fix because X cached the old scrape. Waiting, or posting a URL variant, is the only way around it.
How it differs
A Twitter Card is X's own tag set, while Open Graph is the general one most platforms read. The card adds the layout choice and falls back on Open Graph for the rest. A site with only Open Graph still gets a preview, just in the default layout.
Common errors
Leaving out `twitter:card`. Using an image that is too small. Blocking Twitterbot. Expecting a card to refresh at once. Using a relative image URL. Placing the tags in the body.
In practice
Set `twitter:card` and let Open Graph supply the title, description, and image. Test your most-shared URLs in a draft post, and keep robots.txt open to Twitterbot.