Representational State Transfer Application Programming Interface (REST API) is a stateless, request-response protocol for accessing web services. REST APIs use standard HTTP methods (GET, POST, PUT, DELETE) to interact with resources, making them straightforward and widely supported. The Blockstream Explorer REST API provides on-demand access to Bitcoin and Liquid blockchain data, including blocks, transactions, addresses, and asset information, without requiring applications to run their own full node infrastructure. REST is ideal for queries where applications need specific data at a specific time, such as fetching transaction details, looking up address balances, or retrieving block data. The Blockstream Explorer API combines REST for on-demand queries with RPC for real-time monitoring, giving developers the complete toolkit for building production Bitcoin and Liquid applications.