What Is JSON-RPC?
In blockchain development, JSON-RPC is a popular Remote Procedure Call (RPC) protocol used by blockchain node applications.
JSON-RPC was popularised by the original bitcoind node and then copied to Ethereum. JSON-RPC is human readable and simple protocol for programmatically asking information from your blockchain node.
Querying the current state information
JSON-RPC is used by
Wallets (query tokens, balances)
Decentralised application frontends
You can get a JSON-RPC API for your blockchain application by
Self-hosting a blockchain node and then turning on the JSON-RPC API port
Using a software-as-a-service provider - see ethereumnodes.com for details
Popular alternatives for JSON-RPC includes Protobuf, as used by Cosmos SDK.