Say that launch Pokemon GO was problematic - that's to say nothing. Every time a game appeared in a new region, its servers immediately collapsed, due to which many simply could not get into it. It is even worse when you are about to catch a rare Pokemon and the servers become unavailable.
Currently, Niantic has finally brought them to a more or less stable state, but server crashes are still quite common. If the game won't load or its servers are unavailable, here are some sites that will keep you updated on their status:
Is Pokemon Go Down or Not
A very useful resource that not only monitors the status of the servers, but also checks the delays, the operating time for the past day and week, and how reliably the bait is placed. It also checks the time lag for server log modules for different regions.
Pokemon GO Server Status
A neat little site that has passins to keep you updated. If the servers are buggy, the site will give you the option to turn on notifications, which will then let you know when things are working out.
MMO Server Status
Used to keep track of information for games that are much more complex than Pokemon GO, but have a server status page for that game as well.
