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Paste a URL and see the bubble Instagram will build from it in a DM.
Instagram draws a link as a bubble inside the conversation: the Open Graph image on top, then the title, then the domain, with the description kept short or dropped entirely on narrow screens. The image is the part people react to, so a card whose meaning lives in the description reads as a bare picture here.
The tags it reads are the ordinary ones — og:image, og:title, og:description and og:url. There is no Instagram-specific namespace to set.
Links are only clickable in a few places: direct messages, story stickers, and the link in a profile. Captions and comments render URLs as plain text, so a link pasted into a caption never unfurls no matter how complete the tags are. That is the single most common reason a preview seems missing.
When a DM does show a bare link, the usual causes are a page that blocks the crawler, an og:image behind authentication or a redirect, or a file large enough that fetching it times out. The scan above makes the request as the crawler does, so if the image resolves here it will resolve there.