Validator.nu

monitoring Validator\.nu

Validator.nu HTML validator web crawler

About this crawler

Validator.nu is a web crawler identified by the regular-expression pattern Validator\.nu in the User-Agent request header. It is categorised as monitoring. Use the regex above to detect, log, allow, or block Validator.nu traffic in your web server, CDN edge rules, or robots.txt.

Block-rate · top 25k sites

0.065%
latest snapshot
2026-06-04
matched key: Validator.nu
2026-05-012026-06-040.11%

Technical details

Name
Validator.nu
Pattern
Validator\.nu
Tags
monitoring
Reference
https://validator.w3.org/services
Added
2018/10/14
rDNS suffixes
.validator.nu
Instances
1 known sample(s)

rDNS verification (FCrDNS)

Verify a request is genuinely Validator.nu 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.

Sample User-Agent strings

Validator.nu/LV

Block this crawler

robots.txt — disallow Validator.nu:

User-agent: Validator.nu Disallow: /

Apache .htaccess — return 403:

RewriteEngine On RewriteCond %{HTTP_USER_AGENT} Validator\.nu [NC] RewriteRule .* - [F,L]

Nginx — return 403 inside a server block:

if ($http_user_agent ~* "Validator\\.nu") { return 403; }
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