chain_getBlockHash - Polkadot

Example code for the chain_getBlockHash JSON RPC method. Complete guide on how to use chain_getBlockHash JSON RPC in GetBlock Web3 documentation.

This method returns the block hash for a given block number. If no number is supplied, the hash of the latest block is returned.

Parameters

Parameter	Type	Required	Description
blockNumber	integer or string	No	Block number, as an integer or hex. Defaults to the latest block

Request

cURL

curl --location --request POST 'https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/' \
--header 'Content-Type: application/json' \
--data-raw '{"jsonrpc": "2.0", "method": "chain_getBlockHash", "params": [6754362], "id": "getblock.io"}'

JavaScript

example.js

const response = await fetch('https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
        jsonrpc: '2.0',
        method: 'chain_getBlockHash',
        params: [6754362],
        id: 'getblock.io'
    })
});

const data = await response.json();
console.log(data.result);

Python

example.py

import requests

response = requests.post(
    'https://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/',
    headers={'Content-Type': 'application/json'},
    json={
        'jsonrpc': '2.0',
        'method': 'chain_getBlockHash',
        'params': [6754362],
        'id': 'getblock.io'
    }
)

print(response.json()['result'])

Response

{
    "id": "getblock.io",
    "jsonrpc": "2.0",
    "result": "0x255bc00927df8d33d561792635cbc6bde480a0a505eef5ff28630ece3fc15b32"
}

Response Parameters

Parameter	Type	Description
id	string	Request identifier matching the request
jsonrpc	string	JSON-RPC protocol version ("2.0")
result	string	The 32-byte block hash

Use Cases

• Hash Resolution: Resolve a block number to its hash for other calls

• Pagination: Walk the chain by number, resolving each hash

• Snapshotting: Pin a block hash for consistent state queries

• Explorer Links: Map a height to a linkable block hash

Error Handling

Error Code	Message	Description
-32602	Invalid params	A parameter is missing or has the wrong type or format
-32601	Method not found	The method is not available on this endpoint
-32603	Internal error	The node failed to process the request

Library Integration

The idiomatic way to call Polkadot RPC is the Polkadot.js API (@polkadot/api), which connects over WebSocket and exposes the method as api.rpc.chain.getBlockHash.

polkadot-js.js

import { ApiPromise, WsProvider } from '@polkadot/api';

const provider = new WsProvider('wss://shared.eu-central-1.getblock.io/<ACCESS-TOKEN>/');
const api = await ApiPromise.create({ provider });

const result = await api.rpc.chain.getBlockHash(6754362);
console.log(result.toHuman());