When a page is shared or appears in search results, almost nobody sees the page itself first. They see a title, a short description and an image, assembled by whichever platform is doing the rendering from the meta tags in your HTML. Those few elements decide whether anyone clicks.
The awkward part is that you normally cannot check them until after publishing. Each platform reads your page from its own crawler and caches the result aggressively, so the usual loop is publish, share, discover the description is truncated mid-sentence or the image is cropped through someone's face, fix it, and then fight the cache to see the correction. This tool skips that by rendering the previews locally from values you type.
Three previews are shown because the three platforms behave differently and you cannot infer one from another. A Google result is text-only with its own truncation width. An X card is a wide image with the title and domain beneath. A Facebook or LinkedIn card uses a different aspect ratio and different truncation, and falls back differently when a tag is missing. Seeing all three at once is how you catch a title that fits one and gets cut in another.
The tool also flags the length problems specifically. Titles are truncated by pixel width rather than character count, but around 60 characters is a practical ceiling before a search result starts clipping, and descriptions get cut somewhere near 160. Both limits are approximations that vary with the characters used, which is exactly why looking at a rendered preview beats counting.
Once the values read well, copy the generated tags. The output includes the standard description tag, the Open Graph set used by Facebook, LinkedIn, Slack and most other services, and the Twitter card tags, with absolute image URLs, since a relative image path is one of the most common reasons a card renders with no picture at all.
One limitation worth stating up front: this cannot read the existing tags off a live page. Fetching a URL would require a server-side request, and nothing in this section makes one. You type the values in and the previews render locally from what you typed.