chain_getFinalizedHead - Astar RPC Method

Returns the hash of the last finalized block on Astar. Finalized blocks have been confirmed by the GRANDPA finality gadget and are guaranteed to never be reverted.

Why Astar? Build on Polkadot's leading dApp hub supporting EVM, WASM, and upcoming PolkaVM environments with EVM + WASM + PolkaVM support, Build2Earn developer rewards, dApp Staking, and Soneium cross-layer integration.

When to Use This Method

chain_getFinalizedHead is critical for multi-chain dApp developers, DeFi builders, and teams leveraging Polkadot + Ethereum ecosystems:

• Exchange Deposits — Only credit user funds after the block has been finalized on Astar
• Transaction Confirmation — Verify transactions have achieved irreversible finality for cross-chain DeFi, multi-VM smart contracts, and XCM-enabled interoperability with Ethereum and Cosmos
• Safe Checkpoints — Use finalized blocks as safe anchors for indexing and state queries
• Bridge Operations — Confirm source-chain finality before executing cross-chain transfers

Code Examples

Common Use Cases

1. Exchange Deposit Confirmation

Wait for finality before crediting deposits on Astar:

async function waitForFinality(api, txBlockHash) {
  return new Promise((resolve) => {
    const unsub = api.rpc.chain.subscribeFinalizedHeads(async (header) => {
      const finalizedHash = await api.rpc.chain.getBlockHash(header.number);

      // Check if the transaction block has been finalized
      const finalizedNumber = header.number.toNumber();
      const txBlock = await api.rpc.chain.getBlock(txBlockHash);
      const txNumber = txBlock.block.header.number.toNumber();

      if (finalizedNumber >= txNumber) {
        console.log(`Transaction finalized at block #${txNumber}`);
        unsub();
        resolve(txBlockHash);
      }
    });
  });
}

2. Safe State Queries

Query chain state at the finalized block to avoid reading data that could be reverted:

async function getSafeBalance(api, address) {
  const finalizedHash = await api.rpc.chain.getFinalizedHead();
  const apiAt = await api.at(finalizedHash);
  const account = await apiAt.query.system.account(address);

  return {
    free: account.data.free.toString(),
    reserved: account.data.reserved.toString(),
    finalizedAt: finalizedHash.toHex()
  };
}

3. Finality Lag Monitor

Track the gap between best and finalized blocks for health monitoring:

async function monitorFinalityLag(api, threshold = 10) {
  const bestHeader = await api.rpc.chain.getHeader();
  const finalizedHash = await api.rpc.chain.getFinalizedHead();
  const finalizedHeader = await api.rpc.chain.getHeader(finalizedHash);

  const lag = bestHeader.number.toNumber() - finalizedHeader.number.toNumber();
  console.log(`Finality lag: ${lag} blocks`);

  if (lag > threshold) {
    console.warn(`WARNING: Finality lag (${lag}) exceeds threshold (${threshold})`);
  }

  return lag;
}

Error Handling

Related Methods

• chain_getBlock — Get full block data by hash
• chain_getBlockHash — Get block hash by number
• chain_subscribeFinalizedHeads — Subscribe to finalized block headers
• grandpa_roundState — Monitor GRANDPA finality progress