Slackbot (link unfurling)

User-Agent string

Slackbot-LinkExpanding 1.0 (+https://api.slack.com/robots)

Purpose

Fetches URLs posted in Slack messages to render the unfurl preview inline in the chat. Reads og:* and the page's HTML to produce the rich card.

Quirks

• Caches unfurl content for ~30 minutes.
• Does not honor robots.txt — Slack treats the fetch as a user

action on behalf of the message author.

• Sites can opt out by sending X-Slack-No-Retry: 1 header or

by returning HTTP 401/403.

How to control

<meta property="og:title" content="...">
<meta property="og:image" content="...">
<meta property="og:description" content="...">

To block:

• Return X-Slack-No-Retry: 1 from your server, or
• Return 401/403 to UA matching Slackbot-LinkExpanding.

Sources

• Slack API · Unfurling links