W3C provides various free validation services that help check the conformance of Web sites against open standards.
You are most likely here because this address appeared in logs for your website. This means someone used one of our services to assess content on your site.
While these services were created for the purpose of helping Web developers and designers there is potential like many online services for use other than intended.
Modest traffic from these services does not consitute abuse against your website. Third parties using this service to review content you make publicly available is not substantially different from browsing your site. Web designers frequently evaluate techniques of other websites as a means to learn.
Before considering blocking W3C Validator services you should ensure that nobody in your organization or perhaps contracted by them is requesting our services to make the assessments.
Should you wish to block all or some W3C Validation services from assessing your site you may do so based on our IP addresses or user-agent header string. How to do so varies based on specific operating systems, firewalls and webserver software.
As these services commonly include the link http://validator.w3.org/services in their user-agent you can filter them all based on presence of that string in user-agent header. You can instead opt to block specific Validators based on the unique portion of their user-agents. If you wish to block them individually it would be best not to include the version numbers as those are subject to change.
Traffic from W3C Validator services will be coming from
18.104.22.168/24 subnet and you may firewall or block
that in your web server configuration. You should only firewall
incoming port 80 and 443 from this subnet so as not to block
your users from assessing W3C website or ability to participate
in mailing lists.
Below is a listing of W3C's various Validation services, links to the services themselves, the user-agent header being sent and how to find out more information on each.