Thanks for this suggestion, the messages are actually already customized to be different for each scenarios. But it's true that if you haven't seen the other error messages, it may not be obvious:

• TCP connection timeouts is 10s and is repported as "Connection timeout (10 seconds)"
• A timeout during the TLS handshake is sharing the same 10s delay but reported more precisely as "TLS handshake timeout (10 seconds)"
• Response timeout (can be HTTP response or TCP response for TCP checks) is 30s and reported as "Response timeout (30 seconds)".
• DNS resolutions error/timeout would be reported as "Couldn't resolve host name", sometimes with more details if the DNS resolver provides more details.

Of course there's a lot more codes, including the most common Cloudflare specific ones (520-530) which are manually transformed so you don't have to look them up in the Cloudflare documentation. For example "522 Origin Connection Timed Out (Cloudflare)"

So in your case for an HTTPS check it's a response timeout so the TCP connection and TLS handshake were OK but then updown waited more than 30 seconds without receiving any HTTP response.

Also, if you check the "more details" link on one of the failing requests (from your downtime listing page or from your alert notification), you can see the timings of each step for that particular requests, here is an example from the same error on one of my checks: https://updown.io/downtimes/699f642b63999c7ccb5414b8/results/699f64060de45d5ca98591b4

There we can see the connection and handshake were quick and it's the response that timed out. This can help pinning down the meaning when you're not sure about an error message.

I'm guessing "HTTP response timeout" would have been more obvious ? I can't easily change this because it's shared with other check types like TCP but I can see about splitting this error message into different ones.