The short answer
Slack unfurls from your page's og:title, og:description and og:image. If one is missing, Slackbot is blocked, or previews are turned off, you get a bare link.
Slack has no re-scrape button. Once it caches a URL, editing your tags won't update the card — add a query string like ?v=2 to make Slack treat it as a new link and unfurl fresh.
Want to see the exact og: tags Slack will read before you post? The free slsh.me Open Graph checker fetches your page and renders the card — no Slack, no login.
Why Slack won't unfurl your link.
Slack fails quietly — it just shows the bare URL, with no error. Here's what's actually going on, and the fix for each.
| Cause | What's happening | Fix |
|---|---|---|
| Previews turned off | Link previews are disabled for your account or the whole workspace. | Preferences → Messages & media → enable Show previews of links (an admin controls the workspace-wide toggle). |
| Custom link text | You posted <url|label> or a Markdown [label](url) — Slack suppresses the card for renamed links. | Paste the raw URL on its own so Slack can unfurl it. |
| Wrapped or angle-bracketed | The link sits in a code block, inline backticks, or literal < > brackets. | Post the URL as plain text, outside any code formatting. |
| Missing OG tags | The page has no og:title / og:description / og:image. | Add the core Open Graph tags to the page <head>. |
| Bad og:image | The image URL is relative, behind a login, or too large (Slack skips very heavy images). | Use an absolute https:// image at 1200×630, a few hundred KB. |
| Slackbot blocked | Slackbot-LinkExpanding is denied by robots.txt, a firewall, or a login wall, so it never sees the tags. | Allow Slackbot in robots.txt and serve a public 200 over HTTPS. |
| Stale cache | Slack cached an earlier miss and keeps serving the empty preview. | Append a query string (?v=2) or wait for the ~30-minute cache to expire, then re-share. |
Force a fresh unfurl in three steps.
You've fixed the tags but Slack still shows the old (or empty) card. Because there's no debugger, you bust the cache instead.
Confirm the tags are right first
Check the page returns valid og:title, og:description and an absolute og:image — a standalone Open Graph checker shows exactly what Slackbot will read, without posting to a channel.
Bust Slack's per-URL cache
Slack keys its cache on the exact URL, so add or change a query parameter — ?v=2, ?v=3 — to make it a "new" link. Slack re-fetches and unfurls with your current tags.
Re-share and verify
Post the cache-busted URL. If the card renders, the original URL will also refresh once its ~30-minute cache expires. Still bare? Re-check the causes above — a blocked Slackbot or disabled previews won't be fixed by cache-busting.
Slack has no debugger — check the tags yourself.
There's no "Slack Sharing Debugger." Facebook has one, LinkedIn has the Post Inspector, but Slack ships no public tool to preview an unfurl or force a re-scrape. Your only levers are fixing the tags and busting the cache — blind, unless you can see the tags some other way.
The Open Graph spec is public, so any checker reads what Slack reads. Slack unfurls from the same og: tags every other platform uses, so a standalone checker fetches your page and shows the exact title, description and image Slackbot would — plus the card for X, LinkedIn, Discord, iMessage and WhatsApp in one pass, no login.
The free slsh.me Open Graph checker fetches your page, lists every og: and twitter: tag, runs a best-practices audit, and renders the real card across Slack, X, LinkedIn, Facebook, Discord, iMessage and WhatsApp — no login needed.
Want the card right the first time? Shorten your link on slsh.me and design its Open Graph card in seconds — free.
Questions
Why is my link not unfurling in Slack? +
og:title / og:description / og:image, the og:image is relative or behind a login, Slackbot is blocked in robots.txt or by a firewall, you wrapped the URL in custom link text or a code block, or Slack is serving a cached empty preview. Fix the specific cause and re-share the link.How do I force Slack to refresh a link preview? +
?v=2 — which Slack treats as a new URL and unfurls fresh. Fix your og: tags first, then post the cache-busted URL.Does Slack use Open Graph tags? +
og:title, og:description, og:image and og:site_name — the same tags Facebook and LinkedIn use. It doesn't need twitter:card, though it falls back to it and to oEmbed when Open Graph tags are absent.Why does a link unfurl for me but not for teammates? +
Is there a Slack link preview debugger? +
og: tags Slack would and renders the card, with no login.Ship links that unfurl everywhere.
Shorten any URL with slsh.me and design its Open Graph card — title, description, image — once. It ships valid tags Slack, X, LinkedIn and the rest all read, and you get live click analytics for free.
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