{
  "port": 9944,
  "protocol": "tcp",
  "service": "Substrate / Polkadot JSON-RPC",
  "oneLiner": "A blockchain node built on Parity's Substrate — its JSON-RPC endpoint, serving HTTP and WebSocket on the same port.",
  "whatItIs": "Substrate hardcodes RPC_DEFAULT_PORT = 9944 in substrate/client/cli/src/config.rs, so every node built on the framework — Polkadot, Kusama, parachains, and any `--dev` chain a developer starts locally — listens here by default. Older releases split the endpoint (9944 WebSocket, 9933 HTTP); current ones serve both on 9944. The port carries no IANA registration. Seeing it open means someone is running a node, and a JSON-RPC call like system_chain will tell you which network.",
  "exposure": {
    "verdict": "never",
    "note": "Started with --rpc-external or --rpc-methods=unsafe, the endpoint exposes author_* and system_* methods that can insert keys and reconfigure the node. Keep it bound to localhost and put a method-filtering reverse proxy in front if it must be reachable."
  },
  "checkCommand": "curl -sS -H 'Content-Type: application/json' -d '{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"system_chain\",\"params\":[]}' http://TARGET:9944",
  "links": [
    {
      "title": "polkadot-sdk — substrate/client/cli/src/config.rs (RPC_DEFAULT_PORT)",
      "url": "https://github.com/paritytech/polkadot-sdk/blob/master/substrate/client/cli/src/config.rs",
      "kind": "github"
    },
    {
      "title": "IANA port registry — 9944 (no assignment)",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=9944",
      "kind": "iana"
    }
  ]
}