JSON-RPC: Lightweight Remote Procedure Call Protocol

JSON-RPC is a stateless remote procedure call (RPC) protocol that uses JSON as its data encoding format. It enables applications to invoke methods on remote servers as if they were local, defining a simple message structure with requests, responses, and notifications. Widely adopted in blockchain applications, IoT APIs, and distributed systems, JSON-RPC offers a lightweight alternative to more complex protocols like SOAP or gRPC.

Protocol Fundamentals

• Standardized message structure with jsonrpc, method, params, and id fields
• Transport agnostic: compatible with HTTP, WebSocket, TCP, or other protocols
• Three message types: requests (expecting response), responses, and notifications (no response)
• Structured error handling with standardized codes and custom messages

Benefits of JSON-RPC

• Simplicity: minimalist syntax facilitating implementation and debugging
• Interoperability: JSON readable by virtually all programming languages
• Low overhead: compact payload compared to XML/SOAP
• Native batching: ability to send multiple requests in a single transaction
• Open specification: standardized and community-maintained

Practical Communication Example

// JSON-RPC 2.0 Request
const request = {
  jsonrpc: "2.0",
  method: "user.getProfile",
  params: { userId: 12345 },
  id: 1
};

// Success Response
const successResponse = {
  jsonrpc: "2.0",
  result: {
    userId: 12345,
    name: "Alice Smith",
    email: "alice@example.com"
  },
  id: 1
};

// Error Response
const errorResponse = {
  jsonrpc: "2.0",
  error: {
    code: -32602,
    message: "Invalid params",
    data: "userId must be a positive integer"
  },
  id: 1
};

// Notification (no response expected)
const notification = {
  jsonrpc: "2.0",
  method: "user.logActivity",
  params: { action: "login", timestamp: Date.now() }
  // No 'id' field
};

Implementation Steps

1. Define API contract: list exposed methods and their signatures
2. Choose transport layer (HTTP POST is most common)
3. Implement server with method router and params validation
4. Handle errors using standard codes (-32700 to -32603) and custom ones
5. Add authentication/authorization at transport level (e.g., Bearer token)
6. Document available methods with request/response examples
7. Test with tools like Postman or dedicated JSON-RPC clients

Tools and Libraries

• jayson (Node.js): complete client/server JSON-RPC library
• json-rpc-2.0 (TypeScript): typed implementation with Promise support
• ethereum-rpc (blockchain): JSON-RPC client for Ethereum
• jsonrpcserver/client (Python): toolset for Python 3
• Postman/Insomnia: manual testing with JSON-RPC templates

JSON-RPC establishes itself as a pragmatic solution for distributed architectures requiring simple and efficient communication. Its lightweight nature makes it a preferred choice for microservices, blockchain applications, and IoT systems where bandwidth and integration simplicity are critical. Adopting this protocol reduces infrastructure complexity while maintaining maximum compatibility between heterogeneous systems.