HTML Guide for rate limit

The “HTTP resource not retrievable” error with an HTTP status code of 429 indicates that the W3C Validator was temporarily blocked from accessing a specific URL because the remote server is rate-limiting incoming requests. This typically happens when too many requests are made in a short period of time.

To resolve this:

• Try checking the site at a lower speed, or less often.
• If you’re the server owner, check your server or CDN settings for rate-limiting rules that might be too aggressive.

This error is usually temporary. Waiting before retrying can often resolve the issue.