Published on 2025-08-07T06:18:08Z

Slackbot

Slackbot is a collection of automated bots from the business communication platform Slack. These bots are not traditional web crawlers but on-demand fetchers that activate when users share links or media in Slack. Their primary purpose is to generate the rich link previews that appear in conversations. The most common bot, Slackbot-LinkExpanding, is beneficial to website owners as it makes shared content more engaging and can increase click-through rates.

What is Slackbot?

Slackbot is a family of automated bots from the communication platform Slack. These bots enhance the messaging platform by fetching information from the web when users share links or media. The main bot identifies itself as Slackbot 1.0, but there are also more specialized bots for link expanding (Slackbot-LinkExpanding) and image proxying (Slack-ImgProxy). These bots make HTTP requests to external websites to retrieve content for display within Slack channels.

Why is Slackbot crawling my site?

A Slackbot is visiting your site because a user has shared a link to your content in a Slack channel. The most common visitor is Slackbot-LinkExpanding, which fetches metadata to create a rich preview of the shared link. It looks for oEmbed, Twitter Card, and Open Graph tags. The Slack-ImgProxy bot might visit to fetch and cache an image that was posted. These requests are cached for about 30 minutes to avoid redundant requests. The visits are a direct result of user activity.

What is the purpose of Slackbot?

The purpose of the Slackbot family is to enhance the user experience in Slack by providing rich, visual previews of shared content. The Link Expanding bot creates informative previews with titles, descriptions, and thumbnails. The ImgProxy bot serves a security and performance function by proxying images. Together, these bots create a more engaging communication experience. For website owners, this is beneficial as the previews can increase click-through rates for content shared on the platform.

How do I block Slackbot?

To prevent Slackbots from accessing your site, you can add disallow rules to your robots.txt file. You may want to block them individually. Blocking the link expanding bot will cause links to your site to appear as plain text URLs.

To block the main Slackbot and its link expanding variant, add the following lines to your robots.txt file:

User-agent: Slackbot
Disallow: /

User-agent: Slackbot-LinkExpanding
Disallow: /

How to verify the authenticity of the user-agent operated by Slack?

Reverse IP lookup technique

To verify user-agent authenticity, you can use host linux command two times with the IP address of the requester.
  1. > host IPAddressOfRequest
    This command returns the reverse lookup hostname (e.g., 4.4.8.8.in-addr.arpa.). 
  2. > host ReverseDNSFromTheOutputOfFirstRequest
If the output matches the original IP address and the domain is associated with a trusted operator (e.g., Slack), the user-agent can be considered legitimate.

IP list lookup technique

Some operators provide a public list of IP addresses used by their crawlers. This list can be cross-referenced to verify a user-agent's authenticity. However, both operators and website owners may find it challenging to maintain an up-to-date list, so use this method with caution and in conjunction with other verification techniques.