The official Chia node exposes some RPCs that can be used to query information about the blockchain. FireAcademy.io offers access to full node RPCs, which provide a way of getting information about blocks, coins, mempool transactions, and much more.
API keys are our way of identifying users and tracking how much credits they use. You are free to use API keys as you see fit, but we recommend having one API key per app domain.
Each request to Leaflet consumes a preset amount of credits (420) from the API key owner's account. Credits are billed each week at a known rate ($1 = 4,200,000 credits).
One could think of our credit system as an abstraction layer. Instead of billing for the number of requests made to Leaflet, we chose to go this route to make future product integrations easier.
Something very important to mention is that credits can also be obtained via gift codes, which can be given at the discretion of the almighty admin (also see: grants).
Fun fact: Credits were formerly known as 'traffic' on our old platform, which generated a lot of confusion.