W3C Markup Validator

Verifiable

The W3C Markup Validation Service's fetcher, used when a user submits a URL to be checked for HTML conformance. W3C documents a fixed source address for its validation services alongside the user-agent string.

Operated by World Wide Web Consortium (W3C) · Official documentation

User agents

Patterns this directory matches, with real observed strings.

regexW3C_Validator/[\d.]+
observedW3C_Validator/1.3

How to verify

Documented static ranges: 52.22.66.203/32, 2600:1f18:7d7a:2700::/56

IP ranges (2)

Refreshed daily from the operator's feed. Also available as /data/ips/w3c-validator.ips and /data/bots/w3c-validator.json.

2600:1f18:7d7a:2700::/56
52.22.66.203/32

Good Bot Practices scorecard

Identifies honestly
Stable UA token documented (1 pattern)
Verifiable
Verifiable
Respects robots.txt
Does not honor robots.txt
Behaves
Crawl-rate behavior is operator-declared; not machine-verifiable from this dataset
Reachable operator
Operator and documentation published

Measured against the Good Bot Practices.