As of today, uptime and certificate checks are performed from the following locations:

IP addresses

The full list of IPv4 and IPv6 addresses from where uptime and certificate checks are performed:


As a convenience, these lists are also available as UTF-8 encoded text files:

If your firewall or Network ACL blocks incoming TCP connections, make sure to whitelist these IP addresses to avoid false positives.

User agent

Every HTTP request that servers send has a user agent string which is set to:

Hexadecimal/1.0 (+

To prevent abuse, the user agent string can’t be overwritten.

If you are seeing any malicious traffic coming from this user agent, please get in touch.


If you track visitor data in your web analytics, you might want to exclude requests originating from servers’ IP addresses to get more accurate reporting. You can also filter out requests by the user agent since it is immutable.