Free Kusama RPC (KSM)

Mainnet is the live network: every write is final and carries real value, so it is the right choice once your integration is tested and ready for production traffic, or whenever you only need to read live state such as balances, blocks, or confirmed transactions.

Testnet mirrors the same interface but runs on a network built for experimentation, funded with free test tokens that have no market value. Point your local development environment at testnet first so you can retry failed calls, simulate edge cases, and iterate on contract logic without financial risk, then switch the RPC URL to mainnet once your code is stable.

The interface names shown above (JSON-RPC, Substrate API, REST API) follow different conventions worth knowing before you integrate. JSON-RPC exposes a single HTTP endpoint that accepts method calls in a JSON envelope, and most Web3 libraries speak it natively. REST exposes resources over standard HTTP verbs, which is often simpler for services outside the Web3 stack to consume without a specialized client. gRPC uses binary protobuf messages over HTTP/2, trading a generated client for lower latency and smaller payloads. Pick whichever interface matches the tooling your stack already uses.