chain_getBlockHash - Bridge Hub RPC Method

Returns the block hash for a given block number on Bridge Hub. This is the primary method for converting block numbers into block hashes, which are required by most other chain RPC methods.

Why Bridge Hub? Build on Polkadot's trustless bridging parachain with $75M+ TVL via Snowbridge to Ethereum with on-chain BEEFY/Beacon light clients (no multisigs), 100+ ERC-20 tokens supported, 24+ parachain integrations, and 1-2 minute transfer times.

When to Use This Method

chain_getBlockHash is fundamental for cross-chain developers, bridge operators, and teams requiring trustless Ethereum-Polkadot transfers:

• Historical Queries — Convert block numbers to hashes for state queries at specific heights on Bridge Hub
• Block Navigation — Navigate the blockchain history for trustless ETH and ERC-20 bridging, cross-chain messaging, and parachain-to-Ethereum asset transfers
• Data Indexing — Build block number-to-hash mappings for indexers and explorers
• Cross-Reference — Translate block numbers from events or logs into hashes for detailed lookups

Code Examples

Common Use Cases

1. Block Range Iterator

Iterate over a range of blocks on Bridge Hub for indexing:

async function iterateBlocks(api, startBlock, endBlock) {
  for (let num = startBlock; num <= endBlock; num++) {
    const hash = await api.rpc.chain.getBlockHash(num);
    const block = await api.rpc.chain.getBlock(hash);

    console.log(`Block #${num}: ${block.block.extrinsics.length} extrinsics`);
  }
}

2. Historical State Query

Query Bridge Hub state at a specific block height:

async function getBalanceAtBlock(api, address, blockNumber) {
  const blockHash = await api.rpc.chain.getBlockHash(blockNumber);
  const apiAt = await api.at(blockHash);
  const account = await apiAt.query.system.account(address);

  return {
    blockNumber,
    free: account.data.free.toString(),
    reserved: account.data.reserved.toString()
  };
}

3. Genesis Hash Verification

Verify you are connected to the correct Bridge Hub network:

async function verifyNetwork(api, expectedGenesisHash) {
  const genesisHash = await api.rpc.chain.getBlockHash(0);

  if (genesisHash.toHex() !== expectedGenesisHash) {
    throw new Error(`Wrong network! Expected ${expectedGenesisHash}, got ${genesisHash.toHex()}`);
  }

  console.log('Connected to correct network');
}

Error Handling

Related Methods

• chain_getBlock — Get full block data by hash
• chain_getHeader — Get block header by hash
• chain_getFinalizedHead — Get the latest finalized block hash