W3C-checklink
W3C checklink web crawler for link validation
About this crawler
W3C-checklink is a web crawler identified by the regular-expression pattern W3C-checklink in the User-Agent request header. It is categorised as monitoring. Use the regex above to detect, log, allow, or block W3C-checklink traffic in your web server, CDN edge rules, or robots.txt.
Block-rate · top 25k sites
0.065%
Technical details
- Name
- W3C-checklink
- Pattern
W3C-checklink- Tags
- monitoring
- Reference
- https://validator.w3.org/services
- Added
- 2018/10/14
- rDNS suffixes
.w3.org,.w3c.org- Instances
- 9 known sample(s)
rDNS verification (FCrDNS)
Verify a request is genuinely W3C-checklink 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.
.w3.org.w3c.org
Sample User-Agent strings
W3C-checklink/2.90 libwww-perl/5.64
W3C-checklink/3.6.2.3 libwww-perl/5.64
W3C-checklink/4.2 [4.20] libwww-perl/5.803
W3C-checklink/4.2.1 [4.21] libwww-perl/5.803
W3C-checklink/4.3 [4.42] libwww-perl/5.805
W3C-checklink/4.3 [4.42] libwww-perl/5.808
W3C-checklink/4.3 [4.42] libwww-perl/5.820
W3C-checklink/4.5 [4.154] libwww-perl/5.823
W3C-checklink/4.5 [4.160] libwww-perl/5.823
Block this crawler
robots.txt — disallow W3C-checklink:
User-agent: W3C-checklink
Disallow: /
Apache .htaccess — return 403:
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} W3C-checklink [NC]
RewriteRule .* - [F,L]
Nginx — return 403 inside a server block:
if ($http_user_agent ~* "W3C-checklink") {
return 403;
}
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