How to block Slackbot-LinkExpanding
Operated by Slack. is Slack's link unfurling bot that fetches web page content when users post links in channels, extracting meta tags like oEmbed, Twitter Cards, and… Fetcher Retrieves web page metadata to power app features like link previews or feeds
How it identifies itself
Slackbot-LinkExpanding 1.0 (+https://api.slack.com/robots)
robots.txt
What the agent asks to be told. It obeys this or it does not — nothing enforces it.
User-agent: Slackbot-LinkExpanding Disallow: /
nginx
In the server block, then reload.
# In the server block. 403 rather than 444: a closed connection tells the
# operator nothing, and an agent that gets a status code can log it.
if ($http_user_agent ~* "(Slackbot-LinkExpanding|Slackbot-LinkExpanding 1.0 (+https:|SlackbotLinkExpanding)") {
return 403;
}
Apache
In .htaccess or the vhost.
BrowserMatchNoCase "Slackbot-LinkExpanding" bad_bot
BrowserMatchNoCase "Slackbot-LinkExpanding 1.0" bad_bot
BrowserMatchNoCase "SlackbotLinkExpanding" bad_bot
<RequireAll>
Require all granted
Require not env bad_bot
</RequireAll>
Cloudflare
Security → WAF → Custom rules.
# Security → WAF → Custom rules, action: Block (http.user_agent contains "Slackbot-LinkExpanding") or (http.user_agent contains "Slackbot-LinkExpanding 1.0") or (http.user_agent contains "SlackbotLinkExpanding")
WordPress
A child theme's functions.php, or a small plugin.
// functions.php of a child theme, or a small plugin. Runs before WordPress
// builds the page, so a blocked agent costs one PHP process and no queries.
add_action('init', function () {
$agent = $_SERVER['HTTP_USER_AGENT'] ?? '';
foreach (['Slackbot-LinkExpanding', 'Slackbot-LinkExpanding 1.0', 'SlackbotLinkExpanding'] as $needle) {
if (stripos($agent, $needle) !== false) {
status_header(403);
exit('Blocked: Slackbot-LinkExpanding');
}
}
});
robots.txt is a request. The rules below it are the wall.
Slackbot-LinkExpanding publishes a token, so the directive above will work for as long as it keeps honouring it — and nothing except its own good manners makes it. The server rules match on a header the requester sets, which stops the agent that says who it is and not the one that copies somebody else's name. Botscope verifies identity against DNS and published address ranges, records which check decided each request, and shows you the ones that lied.