Prerender
JavaScript rendering service for search engine crawlers
About this crawler
Prerender is a web crawler identified by the regular-expression pattern Prerender in the User-Agent request header. It is categorised as seo. Use the regex above to detect, log, allow, or block Prerender traffic in your web server, CDN edge rules, or robots.txt.
Block-rate · top 25k sites
0.39%
Technical details
- Name
- Prerender
- Pattern
Prerender- Tags
- seo
- Reference
- https://docs.prerender.io/docs/33-overview-of-prerender-crawlers
- Added
- 2026/05/02
- rDNS suffixes
.prerender.io- Instances
- 3 known sample(s)
rDNS verification (FCrDNS)
Verify a request is genuinely Prerender with forward-confirmed reverse DNS: the client IP's PTR record must end in one of the suffixes below and a forward A/AAAA lookup of that hostname must return the same IP. UA strings alone are spoofable; FCrDNS is not.
.prerender.io
Sample User-Agent strings
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/91.0.4472.114 Safari/537.36 Prerender (+https://github.com/prerender/prerender)
Mozilla/5.0 (Linux; Android 11; Pixel 5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.114 Mobile Safari/537.36 Prerender (+https://github.com/prerender/prerender)
Prerender (+https://github.com/prerender/prerender)
Block this crawler
robots.txt — disallow Prerender:
User-agent: Prerender
Disallow: /
Apache .htaccess — return 403:
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} Prerender [NC]
RewriteRule .* - [F,L]
Nginx — return 403 inside a server block:
if ($http_user_agent ~* "Prerender") {
return 403;
}
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