Glossary
Open Graph
Open Graph is a set of meta tags that tell social platforms, messaging apps and link previews how to present a shared URL: a title, a description, an image and a canonical address. Without them, each platform guesses from the page, and the guess is frequently a logo and the first sentence of a cookie notice. The tags are read by the platform when the link is first shared, and cached afterwards, which is why fixing them later often appears to change nothing.
The tags that matter
`og:title` — the headline of the preview. It may differ from the page title, and usually should be shorter.
`og:description` — one or two sentences. Platforms truncate aggressively, so the first clause carries the weight.
`og:image` — the preview image, given as an absolute URL. This is the tag that determines whether a shared link is noticed at all.
`og:url` — the canonical address of the content, so that shares of parameterised variants consolidate.
`og:type` and `og:site_name` add context, and `twitter:card` controls the layout on the platform that uses it.
The image is the part that goes wrong
It must be an absolute URL. A relative path is the most common failure and produces no image at all.
It must be publicly fetchable without authentication, cookies or a redirect chain, because the platform's own crawler fetches it.
Platforms have minimum dimensions and preferred aspect ratios, commonly around 1200 by 630 pixels for a wide preview. An image below the minimum is ignored rather than scaled up.
File size limits apply, and a very large image is silently dropped by some platforms.
Text inside the image is frequently unreadable at preview size, so an image that is mostly a headline is wasted.
Caching, and why changes seem not to apply
Platforms fetch the tags once and cache the result, often for a long time. Sharing the same URL again shows the cached preview.
Most major platforms provide a debugging tool that re-fetches a URL and clears their cache for it, which is the only reliable way to force an update.
Adding a query parameter produces a different URL and therefore a fresh preview, which is a useful test and a poor permanent solution.
This is why the tags should be correct before a page is widely shared rather than fixed afterwards.
How to check them
`curl -s https://example.com/page | grep -i 'property="og:'` lists the tags in the served HTML.
Confirm the image URL is absolute and returns 200 when fetched on its own, with an image content type.
Tags injected by JavaScript are not seen by most platform crawlers, which do not execute scripts. They must be in the served HTML.
Test with each platform's own preview debugger for the ones that matter to you; behaviour differs enough that one passing does not guarantee another.
Frequently asked questions
- Why does my shared link show the wrong image?
- Usually a cached preview from before the tags were fixed, a relative image URL, or an image below the platform's minimum dimensions.
- Do Open Graph tags affect search rankings?
- No. They control link previews on social platforms and in messaging applications. Search results use the title element and the meta description.
- Can JavaScript set Open Graph tags?
- It can, but most platform crawlers do not execute scripts, so the tags must be present in the HTML the server sends.
Sources
Related
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