Is API to access status of build servers documented?

I found experimentally that the list of all build categories can be 
obtained using this request:
http://{server}/data/.data.json


The list of all builds in one category can be obtained using this request:
http://{server}/data/140amd64-default/.data.json



The per-package status in one build can be obtained using this request:
http://{server}/data/140amd64-default/2c606b8e6de6/.data.json


What I couldn't determine is the query to find all active build servers.
Does such query exist?


Is this API documented anywhere?



Thank you,
Yuri