What is JSON-RPC: A Guide with Example and Comparison

Introduction

JSON-RPC is a lightweight, stateless remote procedure call (RPC) protocol encoded in JSON. It allows data exchange between clients and servers by invoking methods with parameters and receiving results or errors.

As systems become more distributed, the need for simple yet powerful communication protocols has grown. JSON-RPC offers a clean solution for developers who want to avoid the overhead of REST while maintaining a readable and consistent format. Unlike REST APIs, which benefit from clearly defined URLs and a wide range of HTTP libraries, JSON-RPC embeds function calls within the JSON structure, simplifying the communication process and potentially reducing performance bottlenecks.

Let’s explore what JSON-RPC is, how it works, when to use it, and how it compares to alternatives like REST and gRPC.

1. What is JSON-RPC?

JSON-RPC is a protocol that enables communication between systems using JSON-formatted messages. It allows a client to invoke methods on a remote server just like calling local functions.

Consistent implementation and adherence to rules in JSON-RPC are crucial for ensuring uniform interactions with Ethereum nodes.

🧩 Key Characteristics:

• JSON-based: All communication is done using JSON.
• Transport-agnostic: Can run over HTTP, TCP, WebSocket, or other channels.
• Stateless: Each request is independent of the others.
• Versioned: JSON-RPC 1.0 and 2.0 are the official specifications, with 2.0 being the most widely used.

📜 JSON-RPC 2.0 Specification:

Introduced several key features:

• Named parameters
• Batch requests
• Error handling
• Notifications (one-way calls without a response)

2. How JSON-RPC Works

At its core, JSON-RPC defines how method calls are made and results returned. Here's how the interaction looks:

1. Client sends a JSON-RPC request with the method name and parameters.
2. Server processes the request, executes the method, and sends back the result.
3. If an error occurs, the server sends a structured error message instead.

This flow works over any transport layer. JSON-RPC doesn’t mandate HTTP, giving it flexibility across platforms.

3. JSON-RPC Request and Response Structure

✅ Request Format

1{ “jsonrpc”: “2.0”, “method”: “subtract”, “params”: [42, 23], “id”: 1 }

• jsonrpc: Version of the protocol. Specifying the JSON-RPC version is crucial as it ensures compatibility and proper communication between the client and server, affecting the structure and type of responses received.
• method: The remote method to call.
• params: Array or object of parameters.
• id: Unique ID to match requests and responses.

✅ Response Format

1{ “jsonrpc”: “2.0”, “result”: 19, “id”: 1 }
2

The result value is returned in the response format as shown above, highlighting the significance of the data's value in blockchain operations.

❌ Error Format

1
2{ "jsonrpc": "2.0", "error": { "code": -32601, "message": "Method not found" }, "id": 1 }
3

Common error codes:

• -32600: Invalid request
• -32601: Method not found
• -32602: Invalid params
• -32603: Internal error

4. JSON-RPC Example

🧪 Request Example

1{ “jsonrpc”: “2.0”, “method”: “multiply”, “params”: [6, 7], “id”: 2 }

In this example, the integers (INT) 6 and 7 are used as parameters in the JSON request, demonstrating how numerical values are encoded and handled within the Ethereum API framework.

✅ Expected Response

1{ “jsonrpc”: “2.0”, “result”: 42, “id”: 2 }

In the expected response, the data types and return values are often specified in bytes. For example, addresses owned by clients and transaction hashes are encoded in specific byte sizes to ensure correct function execution and transaction verification.

⚠️ Error Handling Example

If the method multiply is not available:

1{ “jsonrpc”: “2.0”, “error”: { “code”: -32601, “message”: “Method not found” }, “id”: 2 }
2

In scenarios where certain operations within the Ethereum network do not yield a result, such as when a block, transaction, or transaction receipt cannot be found, the API will return a 'null' value. This indicates the absence of the requested data and provides clarity on the expected outcomes of these API calls.

5. JSON-RPC vs REST vs gRPC

Feature	JSON-RPC	REST	gRPC
Protocol	JSON over HTTP/TCP	HTTP/HTTPS	HTTP/2
Message Format	JSON	JSON/HTML/XML	Protocol Buffers
Speed	Medium	Medium	High
Human Readable	Yes	Yes	No
Streaming	Limited	No	Yes (bi-directional)
Type Safety	No	No	Yes
Tooling Support	Moderate	Extensive	Advanced (but complex)
Use Cases	Blockchain, RPC APIs	Web APIs	Microservices, IoT

📌 Summary:

• Use JSON-RPC when you want minimal overhead, structured API calls, and don’t need REST’s resource-based model.
• Use REST for public-facing web services with caching, HTTP methods, and standard tooling.
• Use gRPC when performance, streaming, and type safety are critical (e.g., microservices at scale).

6. JSON-RPC API Design

Designing a JSON-RPC API is a critical step in implementing a lightweight remote procedure call (RPC) protocol. A well-thought-out design ensures that the API is intuitive, efficient, and easy to use. When defining method names, it’s essential to choose clear and descriptive names that convey the purpose of the method. Parameters should be well-documented, and the API should support both positional and named parameters to provide flexibility.

Handling multiple calls and notifications is another key aspect. JSON-RPC allows for batch processing, enabling multiple requests to be sent in a single payload. This can significantly improve performance by reducing the number of network round-trips. Notifications, which are one-way calls that do not require a response, can be used for events where the client does not need to wait for a result.

Error handling is crucial for a robust API. JSON-RPC defines a structured error format, allowing the server to return meaningful error messages and codes. This helps clients understand what went wrong and how to address it.

Serialization and deserialization of request and response objects should be efficient to minimize overhead. The API should handle various data types, including integers, strings, and arrays, and ensure that data is correctly encoded and decoded.

Security is paramount. Implementing authentication and authorization mechanisms ensures that only authorized clients can access the API. Input validation is necessary to prevent injection attacks and other vulnerabilities. By considering these factors, you can design a JSON-RPC API that is secure, reliable, and easy to use.

7. Benefits of JSON-RPC

JSON-RPC offers numerous benefits that make it an attractive choice for developers. One of its primary advantages is its simplicity. The protocol is lightweight and easy to understand, making it ideal for remote method invocation in distributed systems. Its flexibility allows it to be implemented in any programming language, providing developers with the freedom to choose their preferred tools.

The protocol supports multiple calls and notifications, enabling efficient communication between clients and servers. This is particularly useful in scenarios where multiple requests need to be processed simultaneously, reducing latency and improving performance.

JSON-RPC’s error handling mechanisms are robust, providing clear and structured error messages that help developers quickly identify and resolve issues. The protocol’s stateless nature means that it does not require server-side session management, making it scalable and efficient.

Another significant benefit is the wide support JSON-RPC enjoys across various programming languages and frameworks. This makes it easy to integrate with existing systems and ensures that developers can leverage their existing knowledge and tools.

Overall, JSON-RPC’s combination of simplicity, flexibility, and robust features makes it a powerful protocol for remote method invocation in a wide range of applications.

6. When to Use JSON-RPC

JSON-RPC is ideal when:

• You need lightweight communication without the full REST stack.
• Your API focuses on actions/functions, not resources.
• You want a clean separation of concerns between client and server.
• You’re working with blockchain nodes (e.g., Ethereum, Bitcoin).
• You need batching and notifications not supported by REST.
• You are interacting with smart contracts and blockchain networks, allowing for operations such as deploying contracts, executing read-only contract functions, and interacting with contracts through various API methods.

7. Limitations of JSON-RPC

Despite its advantages, JSON-RPC has some downsides:

• No support for HTTP verbs (GET, POST, PUT, DELETE) — only method names.
• Smaller ecosystem compared to REST or gRPC.
• Lack of metadata and introspection.
• No built-in authentication or rate-limiting — must be handled separately.
• Challenges in managing dependencies due to the flexible structure of JSON, which can lead to parsing overhead and potential errors when the shape of the requested data is not known beforehand.

8. Popular Use Cases and Real-world Applications

🔗 Blockchain Platforms

Ethereum, Bitcoin, and other blockchain platforms expose JSON-RPC interfaces to interact with nodes, query data, or send transactions.

Additionally, libraries such as the web3 library are available to facilitate calculations and retrieval of storage values in smart contracts.

🔄 Remote Control Systems

JSON-RPC is used in home automation, media servers (like Kodi), and robotics to issue commands to devices. Efficient document processing is crucial in these remote control systems to minimize parsing complexity and overhead, especially when dealing with JSON as the payload format.

🧩 Microservices

Lightweight internal APIs between services that don’t require the complexity of REST or gRPC. Retrieving elements from data structures in microservices can be complex, especially when calculating the storage position of an element in maps.

9. Tools and Libraries Supporting JSON-RPC

🧰 Popular Libraries:

• Python: json-rpc, jsonrpcserver, aiohttp-json-rpc
• Node.js: vscode-jsonrpc, json-rpc-2.0
• Go: github.com/ybbus/jsonrpc
• Java: jsonrpc4j

When considering different data serialization formats, it's important to understand the trade-offs involved. For example, while Protobufs can be more efficient in handling data, they can also be seen as 'foo' due to their implementation complexity and the need for version control. This highlights the balance between ease of use and performance when choosing an encoding method.

⚙️ Integration Tips:

• Use WebSocket for persistent communication.
• Use ID tracking for correlating requests and responses.
• Log all JSON-RPC traffic for debugging.
• To manage APIs in the OpenEthereum environment, you can disable specific APIs by placing a negative sign in front of the API name in the configuration file. This allows for greater control over API exposure based on user preferences.

12. Security Considerations

Security is a critical aspect of implementing a JSON-RPC API. Ensuring that the API is secure and reliable involves several key considerations. Authentication and authorization are fundamental to controlling access to the API. Implementing these mechanisms ensures that only authorized clients can make requests, protecting sensitive data and operations.

Error handling is another important area. The API should provide informative error messages that help clients understand what went wrong without exposing sensitive information. Proper input validation is essential to prevent injection attacks and other vulnerabilities. The API should validate all input parameters and request payloads to ensure they meet expected formats and constraints.

Handling sensitive data securely is crucial. This includes encrypting data in transit and at rest, and securely managing encryption keys and passwords. Implementing rate limiting and IP blocking can help prevent denial-of-service (DoS) attacks by limiting the number of requests a client can make in a given period.

By addressing these security considerations, you can ensure that your JSON-RPC API is secure, reliable, and resilient against potential threats.

14. Troubleshooting

Troubleshooting a JSON-RPC API involves several steps to identify and resolve issues effectively. The first step is to check the API documentation and the request payload to ensure that the API is being used correctly. This includes verifying that method names, parameters, and request formats are accurate.

Next, examine error messages and logs to identify potential issues. JSON-RPC provides structured error messages that can help pinpoint the cause of a problem. Logs are invaluable for tracing the flow of requests and responses, and for identifying where errors occur.

Implementing debugging mechanisms, such as logging and tracing, can greatly aid in troubleshooting. These tools provide detailed insights into the API’s operation, helping developers identify and resolve issues more quickly.

By following these steps, developers can effectively troubleshoot and resolve issues with the JSON-RPC API, ensuring that it remains secure, reliable, and efficient.

Summing Up:

JSON-RPC is a fast, lightweight, and structured RPC protocol suitable for distributed systems, blockchain development, and internal APIs. It simplifies method calls over the network using readable JSON, supports error handling, and is transport-agnostic.

Monitoring the sync status of blockchain nodes is crucial for ensuring that nodes are operating correctly and up-to-date with the latest data. The sync status can either be a detailed object or a simple Boolean value, indicating whether a node is syncing or not.

While it lacks some of the features of REST and the performance of gRPC, JSON-RPC is an excellent choice when you want the best of both — simplicity and functionality.

Choose JSON-RPC when your API is action-oriented and speed is a concern.