See registered build agent machines?

How do I see the list of available build agents from either the CLI or the web interface?

Drone does not keep accounting of agents, since they can be added and removed dynamically, and there is a high probability the list would become out-of-sync. Furthermore, agents use polling which means they frequently connect and disconnect, which makes this number difficult to accurately track. Instead, to get a list of your agents, you should label your agent servers (e.g. in AWS) and then use the AWS API to get a list of all servers. Alternatively, you can use the Drone autoscaler to manage your servers, in which case it can keep track of servers, and provide you with a list.