Open Graph tags control how your links look when shared. This free validator parses your og:* and twitter:* tags, scores them, and — unlike most checkers — verifies the image actually returns 200.
og:title, og:description, og:image, og:url, og:type, plus twitter:card for X. Missing og:title or og:image breaks the preview.
python -m ogcheck https://your-site.com
It exits non-zero on a broken preview, so it doubles as a CI gate.