Let's Encrypt
SSL certificate validation bot verifying domain control for TLS certs
About this crawler
Let's Encrypt is a web crawler identified by the regular-expression pattern Let's Encrypt in the User-Agent request header. It is categorised as scanner. Use the regex above to detect, log, allow, or block Let's Encrypt 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
- Let's Encrypt
- Pattern
Let's Encrypt- Tags
- scanner
- Reference
- https://letsencrypt.org/
- Added
- 2026/04/17
- Instances
- 1 known sample(s)
Sample User-Agent strings
Mozilla/5.0 (compatible; Let's Encrypt validation server; +https://www.letsencrypt.org)
Block this crawler
robots.txt — disallow Let's Encrypt:
User-agent: Let's Encrypt
Disallow: /
Apache .htaccess — return 403:
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} Let's Encrypt [NC]
RewriteRule .* - [F,L]
Nginx — return 403 inside a server block:
if ($http_user_agent ~* "Let's Encrypt") {
return 403;
}
← back to all crawlers