Critical CSS Bot
Extracts critical CSS for web performance optimization tools
About this crawler
Critical CSS Bot is a web crawler identified by the regular-expression pattern Critical CSS Bot in the User-Agent request header. It is categorised as monitoring. Use the regex above to detect, log, allow, or block Critical CSS Bot traffic in your web server, CDN edge rules, or robots.txt.
Block-rate · top 25k sites
No block-rate data for this crawler.
Technical details
- Name
- Critical CSS Bot
- Pattern
Critical CSS Bot- Tags
- monitoring
- Reference
- https://criticalcss.com/
- Added
- 2026/04/26
- Instances
- 1 known sample(s)
Sample User-Agent strings
Critical CSS Bot
Block this crawler
robots.txt — disallow Critical CSS Bot:
User-agent: Critical CSS Bot
Disallow: /
Apache .htaccess — return 403:
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} Critical CSS Bot [NC]
RewriteRule .* - [F,L]
Nginx — return 403 inside a server block:
if ($http_user_agent ~* "Critical CSS Bot") {
return 403;
}
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