W3C's primary web site will soon start redirecting all traffic from http to https, beginning with an 8-hour test on Monday August 1 at 14:00 UTC.
w3.org/blog/2022/07/redirect…
There is no fixed limit, but we recently updated our abuse prevention systems to address an ongoing DDoS attack. If you continue to receive 403 errors you are welcome to send details to sysreq@w3.org
Can you check that your system is accessing the validator using https? The validators are now only available via https as noted on our system status page.