Configuring the Minecraft world border

It's pretty simple, though not obvious as first glance.
In the server.properties file there is a property called max-world-size, and by default it is set to 29999984.
Now you might think this is the best way to change your world border, but it's not. It's literally the maximum size the world border can be. But because it's a server property, it can only be changed by restarting the server.
It's best to just leave this value as-is, and in stead use the worldborder command.

The worldborder can actually be set on-the-fly, like this:
/worldborder set 3000
But beware! This command does not use a radius, but an absolute length. So setting the worldborder to 3000 here, will create a border ranging from -1500 to +1500.
I found this out the hard way and accidentally suffocated 2 players in the process. 😅

You can also find out how big the worldborder currently is:
/worldborder get
It then outputs something like:
The world border is currently 3000 blocks wide
If you did not set a worldborder, but you did change the max-world-size, it will still report its default value. It'll report something like 60.000.000 blocks wide, which can be confusing.