Ethereum JSON-RPC Methods: A Complete Developer Guide

Introduction to Ethereum JSON-RPC

Ethereum's JSON-RPC API enables developers to interact with Ethereum nodes programmatically. This guide covers all essential methods, from querying blockchain data to sending transactions and managing filters.

Core JSON-RPC Features

HEX Value Encoding

Ethereum uses HEX encoding for two primary data types:

1. Quantities (Integers):

   • Format: "0x" + most compact hex representation (e.g., 0x41 for 65)

   • Rules:

     • No leading zeros (0x0400 → invalid)
     • Zero represented as 0x0

2. Unformatted Data (Byte Arrays):

   • Format: "0x" + 2 hex digits per byte (e.g., 0x004200 for 3-byte sequence)

   • Rules:

     • Even number of digits required
     • Empty data: 0x

Default Block Parameter

Several methods accept these block specifiers:

• "latest": Most recent mined block
• "pending": Pending state/transactions
• "earliest": Genesis block
• Block number (HEX string)

Ethereum JSON-RPC Method Reference

Blockchain Methods

eth_blockNumber

Returns the latest block number.

// Request
{
  "jsonrpc":"2.0",
  "method":"eth_blockNumber",
  "params":[],
  "id":83
}

// Response
{
  "result": "0x4b7" // 1207
}

eth_getBalance

Retrieves an account's balance.

Parameters:

1. Address (20-byte)
2. Block parameter

{
  "params": [
    "0x407d73d8a49eeb85d32cf465507dd71d507100c1", 
    "latest"
  ]
}

Smart Contract Interaction

eth_call

Executes a contract call without mining a transaction.

{
  "params": [{
    "to": "0xcontractaddress",
    "data": "0xmethodhash...args"
  }, "latest"]
}

eth_sendTransaction

Creates a new transaction or contract.

{
  "params": [{
    "from": "0xsender",
    "to": "0xrecipient",
    "value": "0xde0b6b3a7640000", // 1 ETH
    "gas": "0x5208" // 21000
  }]
}

Network Methods

net_version

Returns the network ID:

• 1: Ethereum Mainnet
• 3: Ropsten Testnet
• 4: Rinkeby Testnet
• 42: Kovan Testnet

Filter Management

Creating Filters

{
  "method": "eth_newFilter",
  "params": [{
    "topics": ["0x1234..."]
  }]
}

Retrieving Changes

{
  "method": "eth_getFilterChanges",
  "params": ["0xfilterid"]
}

FAQ: Common JSON-RPC Questions

Q: How do I estimate gas costs?

Use eth_estimateGas with your transaction object to get gas estimates.

👉 Learn more about gas optimization

Q: What's the difference between eth_call and eth_sendTransaction?

• eth_call: Read-only, no state changes
• eth_sendTransaction: Writes to blockchain, requires gas

Q: How can I listen for pending transactions?

Create a filter with eth_newPendingTransactionFilter and poll with eth_getFilterChanges.

Advanced Topics

Handling Large Data

When working with contract storage:

// Storage layout calculation
keccak256(abi.encode(key, slot))

👉 Master Ethereum development

Best Practices

1. Always check gas estimates
2. Use batched requests for efficiency
3. Implement error handling for rate limits

Conclusion

This comprehensive guide covers Ethereum's JSON-RPC API essentials. For production applications:

• Always use proper error handling
• Consider client libraries (Web3.js, Ethers.js)
• Monitor node performance

For real-time updates and deeper dives into Ethereum development techniques, bookmark this resource.

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