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Slack link preview: test the unfurl

Paste a URL to see how Slack unfurls it — site name, title, description and image — without posting into a channel. Slack publishes no image limits; the check shows what other platforms require.

No signup, no Slack login. We fetch the page the way a crawler does (HTML only, no JavaScript) and do not store the URL.

What Slack needs

MinimumAspect ratioMax file sizeFormats
Slack Not documented Not documented Not documented Not documented

Values from the platform's own documentation, checked 2026-11-02 (all platforms: OG image size). Sources: · Slack API: Slackbot and robots

Tags Slack reads

Slack link preview not showing or not updating?

  1. Slack keeps an unfurl for a while (about 30 minutes). Add a query string to see a new one sooner.
  2. Allow Slackbot-LinkExpanding in robots.txt and your bot protection.
  3. No unfurl at all? A workspace admin can turn unfurling off for some domains, and a user can remove an unfurl from a message.
  4. Print the tags in the server HTML; the unfurl is built without JavaScript.

A preview image for every page, on Slack and everywhere else

Most broken previews have no image at all. Shareglint renders one for every page from its title — one meta tag, no code — at a size that passes every documented limit (the sizes). 100 images a month free.

Start free — 100 images a month OG images without code

Questions

How does Slack unfurl links?

Slack's crawler fetches the URL and builds the preview from oEmbed or the Twitter Card and Open Graph tags: site name, title, description and image.

How do I add extra fields to a Slack unfurl?

Use twitter:label1 and twitter:data1 (and label2/data2) meta tags. Slack shows them as label–value pairs under the preview.

Why does Slack show an old preview?

Slack caches unfurls for a short time. Wait, or share the URL with a query string.