# W3C Validation Services

Providing standards conformance checking services to the Web community

## W3C Validation Services

### Table of contents

### About W3C Validation services

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 evaluate content on your site.

### Misuse

While these services are intended to help web developers, it is possible they may be abused.

Modest traffic from these services does not constitute 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.

### Blocking W3C Validators

Before considering blocking requests from W3C's validator services you should ensure that nobody in your organization is using them to review your site.

Should you wish to block W3C's validation services from accessing 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.

#### Blocking on User-Agent

As these services commonly include `https://validator.w3.org/services` in their user-agent header you can filter them based on presence of that string. 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.

#### Blocking on IP Address

Traffic from W3C validators and our other services will be coming from `52.22.66.203` (IPv4) or `2600:1f18:7d7a:2700::/56` (IPv6). To avoid receiving requests from these services you can update your firewall or web server configuration to block traffic from those addresses. You should only block incoming requests on port 80 and 443, so as not to block your users from accessing the W3C website or participating in W3C mailing lists.

### W3C Validation Services

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.

- #### Markup Validator

  - Service
  - User-Agent: `W3C_Validator/1.3`
  - About

- #### Validator.nu

  - Service
  - User-Agent: `Validator.nu/LV`
  - About

- #### Link checker

  - Service
  - User-Agent: `W3C-checklink`
  - About
  - * as a crawling service this honors robots.txt directives

- #### Internationalization Checker

  - Service
  - User-Agent: `W3C_I18n-Checker/1.0`
  - About

- #### Feed Validation

  - Service
  - User-Agent: `FeedValidator/1.3`
  - About

- #### CSS Validator

  - Service
  - User-Agent: `Jigsaw/2.3.0 W3C_CSS_Validator_JFouffa/2.0`
  - About