How to tell when server is up and running after backgrounded or startup

[sainttttt]

I was wondering how I can verify that the server is totally up and running after resuming from being backgrounded or from startup. Right now I'm trying to locally run a website that locally serves pdfs and it seems that if I just try to immediately load I get issues. I'm doing a hacky fix of manually having timers to wait before making requests, but it would be really helpful if there was some event which I could find which would say when it's actually running or available or not. Is this possible at all or am I going about this totally wrong? Thanks!