404 Checker
404 link checker service
About this crawler
404 Checker is a web crawler identified by the regular-expression pattern 404 Checker in the User-Agent request header. It is categorised as monitoring. Use the regex above to detect, log, allow, or block 404 Checker traffic in your web server, CDN edge rules, or robots.txt.
Block-rate · top 25k sites
0.26%
Technical details
- Name
- 404 Checker
- Pattern
404 Checker- Tags
- monitoring
- Reference
- http://www.404checker.com/user-agent
- Added
- 2026/05/09
- Instances
- 1 known sample(s)
Sample User-Agent strings
404 Checker [http://www.404checker.com/user-agent]
Block this crawler
robots.txt — disallow 404 Checker:
User-agent: 404 Checker
Disallow: /
Apache .htaccess — return 403:
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} 404 Checker [NC]
RewriteRule .* - [F,L]
Nginx — return 403 inside a server block:
if ($http_user_agent ~* "404 Checker") {
return 403;
}
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