# Slack Link Preview Checker — Test Your Unfurl Free

> 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.

Page: https://shareglint.com/en/tools/slack-link-preview

## What Slack needs

- Slack reads oEmbed, Twitter Card and Open Graph tags: `og:site_name`, `og:title`, `og:description`, `og:image`.
- `twitter:label1`/`twitter:data1` (and 2) add short label–value pairs under the unfurl, such as "Reading time · 6 min".
- Slack fetches links with `Slackbot-LinkExpanding`.
- Slack documents no image size or file limit.

## Slack link preview not showing or not updating?

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

## 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.