CriticalCSSBot is a bot in the monitoring and analytics bots category, operated by Critical CSS.
We operate a SASS for website optimisations, we have thousands of customers. Some of them use Cloudflare but I don't have access to any exact list.
Monitoring bots check uptime, performance and page changes on behalf of a site owner or a third party. Allow the services you run yourself and exclude them from analytics so they do not inflate page views.
CriticalCSSBot identifies itself with this user agent string:
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.0 Safari/537.36 Criticalcss.com/2.0.0Anyone can copy a user agent string. Transfon Security also checks where each request comes from, so a request that claims to be a known crawler but comes from the wrong network is treated as a fake, not as the real crawler.
We have not confirmed whether CriticalCSSBot follows robots.txt. Add a rule, then check your logs to see that it stopped. robots.txt is a plain text file at the root of your domain, such as https://example.com/robots.txt.
User-agent: CriticalCSSBot Disallow: /
User-agent: CriticalCSSBot Disallow: /private/ Disallow: /search
User-agent: CriticalCSSBot Allow: /blog/ Disallow: /
User-agent: CriticalCSSBot Allow: / User-agent: * Disallow: /
User-agent: CriticalCSSBot group, CriticalCSSBot ignores your User-agent: * rules, so repeat any that should still apply.CriticalCSSBot from CriticalCSSBot's user agent; check Critical CSS's own documentation if it publishes a different robots.txt name.Treat robots.txt as a statement of your policy, and enforce it where requests arrive.
Allow CriticalCSSBot if it is a service you use, and keep its visits out of page views and ad requests either way.
Transfon Security for publishersCriticalCSSBot is not a person. Exclude it from campaign and conversion data so reports reflect real visitors.
Transfon Security for advertisersAllow CriticalCSSBot only if it works for your store, and keep it away from cart and checkout.
Transfon Security for e-commerceIf CriticalCSSBot is a service you use, allow it on the endpoints it needs and block it elsewhere.
Transfon Security for SaaS and APIsrobots.txt is a request, not an enforcement. Transfon Security shows CriticalCSSBot by name in the Top Bots report, so you can see how often it visits and which pages it reads. Block or allow it with a User Agent rule, or slow it down with a rate limit decision rule.
Transfon Security
CriticalCSSBot is a bot in the monitoring and analytics bots category, operated by Critical CSS. We operate a SASS for website optimisations, we have thousands of customers. Some of them use Cloudflare but I don't have access to any exact list.
We have not confirmed whether CriticalCSSBot follows robots.txt. Add a robots.txt rule, then check your logs to see that it stopped, and block it by user agent if it did not.
Add "User-agent: CriticalCSSBot" followed by "Disallow: /" to the robots.txt file at the root of your site. To enforce it, block requests whose user agent contains "Criticalcss.com/" at your WAF. In Transfon Security that is one User Agent block rule.
No. robots.txt is voluntary, so CriticalCSSBot may not follow it, and anyone can send CriticalCSSBot's user agent, so a fake CriticalCSSBot ignores your rule. Enforce the rule where requests arrive, at your WAF, and check the source network.
Monitoring bots check uptime, performance and page changes on behalf of a site owner or a third party. Allow the services you run yourself and exclude them from analytics so they do not inflate page views.
Transfon Security identifies every bot in this directory in your traffic reports, flags fake search crawlers, and lets you allow, block or rate limit each bot.
Privacy, security, monetization, and performance insights. A few emails a month, no spam.