Slack image sizes for link unfurls

Last updated: September 20, 2026.

Size figures on this page are placeholders. They are not marked verified because we have not re-checked Slack’s current documentation.

Slack unfurls a public URL when someone pastes it in a channel or DM. The client fetches Open Graph (and sometimes Twitter Card) tags and draws a compact attachment. There is no separate Slack image format. This page covers that unfurl — not file uploads or Slack canvases. Pixel values stay unverified placeholders until we re-check Slack’s link-unfurling docs. A 1200×630 PNG that already works for Facebook is the usual starting point. Workspace apps can customize unfurls via the API; this guide is about the default HTML scrape.

Recommended Slack size

Slack recommended image sizes
PlatformImage typeRecommended sizeAspect ratioMax file size
SlackLink unfurl1200 × 630 px1.91:15 MB

Official page to re-check:https://api.slack.com/reference/messaging/link-unfurling

How Slack crops your image

Unfurls are compact. Slack shows a landscape thumbnail beside title and description. Edge-hugging type that looks fine at full OG size can vanish at chat width. Keep the headline in the center band with fewer words than a Facebook card.

If og:image is portrait, Slack will center-crop for the thumbnail. Prefer a 1.91:1 file for URLs you expect people to paste in Slack.

Slack caches unfurls. Changing the image at the same path often leaves the old card until the link is pasted again in a fresh message after cache expiry.

Three common Slack mistakes

  • Private or login-walled pages

    Slack’s crawler cannot sign in. Staging hosts, SSO walls, and cookie gates produce title-only or empty unfurls. Test on a public 200 HTML response.

  • Relative og:image URLs

    Slack needs an absolute https URL that returns 200 without cookies. Relative paths fail the same way they fail on Facebook.

  • Blocking unknown user agents

    Aggressive bot filters that drop Slackbot will hide the image. Allow anonymous GET on both the page and the PNG.

Unfurls versus custom apps

Default unfurls read meta tags. Custom Slack apps can replace that card with Block Kit content. If your team uses an app that overrides unfurls, fixing og:image on the site will not change what Slack shows until the app is updated.

There is no consumer “Slack debugger” like Facebook Sharing Debugger. Confirm tags in View Source, then paste the URL in a test channel. Use the [link preview checker](/link-preview-checker/) to inspect the first HTML response.

Create a Slack-friendly OG image

Opens the generator with the Slack size preset selected. Nothing is uploaded.

Frequently asked questions

Short answers about Slack preview images.

What size should a Slack link unfurl image be?

Use a landscape Open Graph file around 1200×630 pixels. Slack does not publish a separate required size for default unfurls. Keep type inside a safe margin so the thumbnail still reads.

Why does Slack show a link with no image?

Usually a missing or relative og:image, a blocked fetch, or a page the crawler cannot reach. Fix the public HTML and image URL, then paste the link in a new message.

Does Slack use Twitter Card tags?

It may fall back to them, but Open Graph is the reliable contract. Set one absolute og:image and test the live URL.

Can I use the same file as Facebook?

Yes. One 1200×630 PNG usually serves Slack, Facebook, LinkedIn and WhatsApp. Change the path when you revise the artwork so caches refresh.