Slack Green

Slack link preview checker

Check why a link shows no preview in Slack, or the wrong one. Paste a URL and see the card Slack will show, built from the page the way Slackbot fetches it, with the rules we measured in Slack: a title alone gives no card, HTML in a description drops it, and twitter:card summary hides the image.

What Slack shows

you4:39 PM
https://example.com/blog/release-notes
Release notes: tables, themes and faster search
Paste a table from Sheets and it stays a table. Plus 4 new themes and search that finds threads.
Acme blog

Why

  • Slack shows a card. Drawn above the way Slack for web drew our test pages.
  • Title from og:title. Slack takes og:title, then twitter:title, then <title>. It keeps the whole title and cuts it at the end of one line.
  • Description from og:description. The card shows the first 2 lines of it.
  • twitter:card is summary, so Slack hides the image. In 3 of 3 tests a page with twitter:card summary got no image, whatever the image. Use summary_large_image.

Edit the card

<meta property="og:title" content="Release notes: tables, themes and faster search">
<meta property="og:description" content="Paste a table from Sheets and it stays a table. Plus 4 new themes and search that finds threads.">
<meta property="og:image" content="https://pcpcicvhrcazmlpjrqho.supabase.co/storage/v1/object/public/blog-images/how-to-make-a-table-in-slack/tbl-paste-chip.png">
<meta property="og:site_name" content="Acme blog">
<meta name="twitter:card" content="summary">

Fixed the page and Slack still shows the old card? Slack reused its card when we posted the same URL again, and fetched a URL with a new query string. Put the tags at the top of <head>, before any script.

What Slack reads

whole page (Range unknown)
titleog:titleog:descriptionog:imageog:site_nametwitter:card

Not to scale. Green tags are read. Slack also shows at most 5 cards per message.

How to fix a Slack link preview

  1. Paste the URL under Check a URL and click Check link. For a page behind a login, open Paste HTML and paste its source.
  2. Read the card on the left. It is drawn the way Slack for web draws it: one line of title, two lines of description, the site name and a thumbnail 106 px high.
  3. Fix every red line under Why. Each one names the rule from our tests and what to change.
  4. Try a new title, description or image in Edit the card, then click Copy meta tags and put them at the top of the page head.
  5. Post the link again with Copy a link Slack fetches again. Slack reused its old card when we posted the same URL twice.

Frequently asked questions

Why does my link show no preview in Slack?

In our tests on 9 October 2026 Slack showed no card when the page had only a title (og:title, twitter:title or <title>), when the description held an HTML tag, when the page answered 404 or 500, after more than 3 redirects, and when the page took 30 s. A page with a description or a usable image always got a card.

Why is the image missing from my Slack preview?

Three causes showed up in our tests. twitter:card set to summary hid the image every time. With a description, an image 201 px wide or less was dropped and 202 px showed; Slack reads the real pixels, not og:image:width. And SVG images never showed, while PNG, JPEG, GIF and WebP did.

How do I make Slack refresh an old link preview?

Change the URL. When we posted the same URL again 3 minutes after changing the page, Slack showed the old card and did not fetch the page. The same URL with a new query string, like ?v=2, was fetched again and showed the new card.

Does Slack read the whole page?

It asks for the first 32 KB (Range: bytes=0-32768). If your server sends the whole page anyway, Slack reads it: tags after 3 MB of script were found. If your server answers the Range request, Slack next asks for byte 65,536 onward, so tags between 32 KB and 64 KB are never read. Put the tags first in <head>.

Which tags does Slack use for the title and description?

og:title first, then twitter:title, then <title>; og:description first, then twitter:description, then the meta description. Slack keeps the whole title on one line with an ellipsis and cuts the description at 700 characters. og:site_name replaces the domain under the text. theme-color and twitter:label tags are not shown.

Related reading

Slack Green does one thing: it keeps your Slack presence dot green while you are actually working, so a quiet keyboard does not mark you away. Try it free.