chain_getHeader - JSON-RPC Method

Description

Retrieves the header of a specific block without the body (extrinsics). This JSON-RPC method is more efficient than chain_getBlock when you only need header information like parent hash, block number, and state root.

Parameters

Parameter	Type	Required	Description
blockHash	string	No	Hex-encoded block hash. If omitted, returns the latest block header

Returns

Field	Type	Description
parentHash	string	Hash of the parent block
number	string	Block number (hex-encoded)
stateRoot	string	Root of the state trie after executing this block
extrinsicsRoot	string	Root of the extrinsics trie
digest	object	Digest items (consensus messages, seal, etc.)

Request Example

{
  "jsonrpc": "2.0",
  "method": "chain_getHeader",
  "params": [],
  "id": 1
}

Response Example

{
  "jsonrpc": "2.0",
  "result": {
    "parentHash": "0x4a84d1c5fc5c725b26a3c8e126d8f65e1c2d2dc5b3fcbc91e67e7637fa136789",
    "number": "0x123456",
    "stateRoot": "0x8f7a82e2e0f3e73f5e232e68de18144f6e7a52a6db39bb5e5e3d9ca6e1f72845",
    "extrinsicsRoot": "0x2e6f9a7d2c4b3e1a8f5c6d9e4b1a7c3f8e5d2a9b6c4e1f8a5d3c2b9e7f6a4d38",
    "digest": {
      "logs": [
        "0x0642414245b501013c0000009d2ef70f00000000",
        "0x054241424501019e7b3c4e1f8a2d5c6b9e4f3a7d2c5e8b1f4a6d9c3e2b5f8a7c4d"
      ]
    }
  },
  "id": 1
}

Code Examples

JavaScript

const getHeader = async (blockHash = null) => {
  const params = blockHash ? [blockHash] : [];
  
  const response = await fetch('https://api-polkadot.n.dwellir.com', {
    method: 'POST',
    headers: {
      'Authorization': 'Bearer YOUR_API_KEY',
      'Content-Type': 'application/json'
    },
    body: JSON.stringify({
      jsonrpc: '2.0',
      method: 'chain_getHeader',
      params: params,
      id: 1
    })
  });
  
  const data = await response.json();
  return data.result;
};

// Get latest header
const header = await getHeader();
console.log('Latest block:', parseInt(header.number, 16));

Python

import requests
import json

def get_header(block_hash=None):
    url = "https://api-polkadot.n.dwellir.com"
    headers = {
        "Authorization": "Bearer YOUR_API_KEY",
        "Content-Type": "application/json"
    }
    
    params = [block_hash] if block_hash else []
    
    payload = {
        "jsonrpc": "2.0",
        "method": "chain_getHeader",
        "params": params,
        "id": 1
    }
    
    response = requests.post(url, headers=headers, data=json.dumps(payload))
    return response.json()["result"]

# Get header info
header = get_header()
block_number = int(header["number"], 16)
print(f"Block #{block_number}")
print(f"Parent: {header['parentHash']}")
print(f"State Root: {header['stateRoot']}")

Use Cases

1. Light Clients: Verify chain without downloading full blocks
2. Block Monitoring: Track new blocks with minimal data transfer
3. Fork Detection: Compare parent hashes to detect chain reorganizations
4. State Verification: Validate state roots for merkle proofs

Related Methods

• chain_getBlock - Get full block with extrinsics
• chain_getBlockHash - Get block hash by number
• chain_subscribeFinalizedHeads - Subscribe to finalized headers