Blockchain API Tutorial: Architectures, Verification, Smart Contracts, and Distributed Systems Blockchain APIs are often introduced as simple interfaces for querying balances, sending transactions, or interacting with smart contracts. That framing is technically correct, but it misses the deeper reality. A blockchain API is not merely a gateway into a database — it is an interface into a distributed consensus system operating under adversarial conditions. Traditional APIs expose mutable centralized state controlled by a single authority.