Shareability · 18 points
twitter:card
One check, stated three ways: what we measure, what would make it wrong, and how to confirm it yourself.
What this measures
Whether twitter:card is present and whether it asks for a large image.
Where this check can be wrong
X derives a card from Open Graph when this tag is absent, so a missing twitter:card often renders correctly anyway. We report the declaration you control, not the guess.
Verify it without taking our word for it
Grep the head for twitter:card, then use X's Card Validator on the live URL.