Slack Link Preview Not Updating? How to Fix Stale OG Data

Slack showing an old title, wrong image, or no preview at all? Here's how Slack's Unfurl bot works and the exact steps to fix stale or missing link previews.

How Slack fetches link previews

When you paste a URL into Slack, the Slackbot Unfurl crawler (identified as Slackbot-LinkExpanding in its User-Agent) fetches the page to extract OG metadata. Slack then caches that result. If your tags were wrong at the time of the first fetch, you may see stale previews even after fixing the underlying HTML.

Quick fix checklist

  1. Verify your OG tags are present and correct: Slack reads og:title, og:description, og:image, and og:url. Check these exist in your page's <head>.
  2. Use an absolute image URL: og:image must be a full https:// URL. Relative paths will not work.
  3. Bust the Slack cache by re-pasting the link: Slack re-fetches when you delete the existing unfurl and paste the URL again. Try deleting your old message and pasting the link fresh in a new message.
  4. Add a cache-buster query parameter: if the same URL keeps showing the old preview, try appending a dummy param like ?v=2 to force Slack to treat it as a new URL and re-fetch metadata.
  5. Check your image is publicly accessible: paste the image URL directly into an incognito browser. If you hit a login page or error, Slack cannot load it.
  6. Confirm Slackbot is not blocked in robots.txt: check that your robots.txt does not disallow Slackbot or all bots.
  7. Ensure OG tags are in server-rendered HTML: Slack's crawler does not execute JavaScript. Tags injected by client-side frameworks will not be picked up — they must be in the raw HTML response.
  8. Check for HTTPS and mixed-content issues: Slack may refuse to display images served over HTTP when the page is HTTPS. All asset URLs should use https://.

Slack image requirements

  • Recommended size: 1200×630 px (or 1.91:1 aspect ratio)
  • Minimum size: 200×200 px (below this Slack may skip the image)
  • Supported formats: JPEG, PNG, GIF
  • File size: keep under 5 MB for reliable rendering
  • Content-Type: server must return correct MIME type (e.g., image/png)

Slack shows no preview at all — what to check

If Slack shows no unfurl (no title, no image, no description), the most common causes are:

  • Link unfurling is disabled in the Slack workspace settings. Workspace admins can turn off link previews globally or per-domain. Ask your admin to check Settings & Permissions → Messages & Media → Show link previews.
  • The URL is on Slack's blocklist. Certain domains and URL patterns are never unfurled (e.g., shortened URLs without valid OG tags, known spam domains).
  • The page returns a non-200 status code. A 301/302 that eventually resolves to the right page may still confuse Slack's crawler. Verify the final destination returns 200.
  • The page requires authentication. Slack cannot log in. Your preview page must be publicly accessible.

Paste your URL into OG Fixer to instantly see what Slack and other platforms will show — and generate a corrected OG image if needed.

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