What Open Graph and Twitter Card Tags Are
Open Graph tags (og:title, og:description, og:image, og:url, og:type, og:site_name) are meta tags that control how a link looks when shared on Facebook, LinkedIn, Slack, Discord, and most other platforms, a title, description, and preview image instead of a bare URL. Twitter Card tags (twitter:card, twitter:title, twitter:description, twitter:image, twitter:site) serve the same purpose specifically for X (formerly Twitter), and per Twitter's own convention, silently fall back to the equivalent Open Graph tag when the Twitter-specific one is missing, which is why a page with just Open Graph tags still gets a reasonable-looking X preview.
Reading the Completeness Score
The score reflects how many of the five most consequential tags are present: og:title, og:description, og:image, og:url, and twitter:card. A missing og:image is the highest-impact gap in practice, since a link shared without a preview image gets dramatically less engagement on almost every platform; a missing og:url matters less in practice since most platforms fall back to the actual page URL when it's absent, but including it explicitly avoids relying on that fallback.
How Twitter Card Fallback Works
If twitter:title, twitter:description, or twitter:image aren't present, this tool (matching real platform behavior) falls back to the corresponding og:title, og:description, or og:image value instead of leaving the preview blank. twitter:card itself (which controls the card layout, usually summary or summary_large_image) has no Open Graph equivalent and must be set explicitly if you want a specific card layout rather than a platform default.
Testing a Page Before It's Deployed
Most Open Graph preview tools require a live, publicly reachable URL to fetch and inspect. This tool works directly from pasted HTML source instead, so a page still in local development, behind authentication, or on a staging environment not yet publicly accessible can still be checked, just paste the rendered HTML (view-source or a browser's dev tools Elements panel both work) before it ever goes live.
Common Mistakes
The most common issues are a missing og:image entirely, an image with the wrong aspect ratio for the intended card size (roughly 1.91:1 for a large summary card, which most platforms recommend), duplicate or conflicting meta tags from a CMS plugin stacking on top of manually-added tags, and forgetting that most platforms cache a link's preview the first time it's shared, meaning a fix won't show up until the platform's cache is manually refreshed (each platform has its own debugger/cache-clearing tool for this). As an og tag checker and social share preview tool, it works as an og title description checker, a meta tag preview, a facebook share preview and linkedin share preview, an open graph validator, and a social media card tester before a link ever gets shared.