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Overview

Flashblocks enable up to 200 millisecond transaction confirmations on Base by leveraging preconfirmations, ultra-fast signals that arrive before the next block is sealed. Built for developers who demand instant UX, it’s ideal for high-frequency apps, games, and real-time interactions where waiting even a few seconds is too long. By integrating directly within Base’s infrastructure, Flashblocks enables, seamless, ultrafast and snappy user experiences without compromising security.

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Integrating Flashblocks

Flashblocks is enabled for developers on Base. There are two ways you can integrate with Flashblocks data. You can either use the WebSocket API to stream real-time block updates, or use the RPC API to query the Flashblocks-aware RPC endpoint.

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RPC API

Base offers the following public Flashblocks aware RPC endpoints. These are rate limited and may not be suitable for production use - we recommend using a node provider that runs Flashblocks integrated nodes. Major node providers such as Alchemy, Infura, QuickNode and dRPC have Flashblocks-aware RPCs that can be leveraged

NetworkURL
Mainnethttps://mainnet-preconf.base.org
Sepoliahttps://sepolia-preconf.base.org

The following RPC methods can return Flashblocks specific data. All standard Ethereum JSON-RPC methods are still supported as usual.

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eth_getBlockByNumber

Use the pending tag to retrieve the latest Flashblock:

curl https://sepolia-preconf.base.org -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["pending",true],"id":1}'

Example Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "number": "0x1234",
    "hash": "0x...",
    "transactions": [...]
  }
}

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eth_getTransactionReceipt

Use the existing receipt RPC to get preconfirmed receipts:

curl https://sepolia-preconf.base.org -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getTransactionReceipt","params":["0x..."],"id":1}'

Example Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "transactionHash": "0x...",
    "blockNumber": "0x1234",
    "status": "0x1"
  }
}

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eth_getBalance

Use the pending tag to get the address balance in the latest Flashblock:

curl https://sepolia-preconf.base.org -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getBalance","params":["0x...","pending"],"id":1}'

Example Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x0234"
}

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eth_getTransactionCount

Use the pending tag to get the address nonce in the latest Flashblock:

curl https://sepolia-preconf.base.org -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getTransactionCount","params":["0x...","pending"],"id":1}'

Example Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "0x1b" // 27 transactions
}

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eth_getTransactionByHash

Use the existing get transaction by hash RPC to get preconfirmed transactions:

curl https://sepolia-preconf.base.org -X POST -H "Content-Type: application/json" -d '{"jsonrpc":"2.0","method":"eth_getTransactionByHash","params":["0x..."],"id":1}'

Example Response

{
  "type": "0x2",
  "chainId": "...",
  "nonce": "...",
  ...
}

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Libraries

For popular libraries, they sometimes require additional RPC support for transaction preconfirmation to work properly. We are working on adding Flashblocks support to the following libraries:

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Ethers

  const providerA = new ethers.JsonRpcProvider(
    "https://sepolia-preconf.base.org"
  );

  const wallet = new ethers.Wallet(process.env.PRIVATE_KEY, providerA);

  try {
    // Create a simple transaction (sending 0.001 ETH to a random address)
    const tx = {
      to: "<SOME ADDRESS>",
      value: ethers.parseEther("0.0000001"),
    };

    // Submit transaction
    const submissionTime = new Date();
    const transaction = await wallet.sendTransaction(tx);

    console.log(`Submitting transaction at: ${submissionTime.toISOString()}`);
    console.log(`Transaction hash: ${transaction.hash}`);

    await transaction.wait(0); // Make sure to set the confirmation count to 0

    console.log("Transaction confirmed");
    const confirmationTime = new Date();
    console.log(`Transaction confirmed at: ${confirmationTime.toISOString()}`);
    console.log(`Time difference: ${confirmationTime - submissionTime}ms`);
  }

You should see the confirmation time significantly lower than the standard RPC endpoint.

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Viem/Wagmi

// Create wallet client
  const account = privateKeyToAccount(`0x${process.env.PRIVATE_KEY}`);
  const walletClient = createWalletClient({
    account,
    chain: {
      id: 84532,
      name: "base-sepolia",
      network: "base-sepolia",
    },
    transport: http(
      "https://sepolia-preconf.base.org"
    ),
  });

  // Create public client for waiting
  const publicClient = createPublicClient({
    chain: {
      id: 84532,
      name: "base-sepolia",
      network: "base-sepolia",
    },
    transport: http(
      "https://sepolia-preconf.base.org"
    ),
  });

  try {
    const submissionTime = new Date();
    console.log(`Submitting transaction at: ${submissionTime.toISOString()}`);

    // Send transaction
    const hash = await walletClient.sendTransaction({
      to: "<SOME ADDRESS>",
      value: parseEther("0.0000001"),
    });
    console.log(`Transaction hash: ${hash}`);

    // Wait for transaction to be mined
    const receipt = await publicClient.waitForTransactionReceipt({ hash });
    const confirmTime = new Date();

    console.log(`Transaction mined at: ${confirmTime.toISOString()}`);
    console.log(`Time difference: ${confirmTime - submissionTime}ms`);
  } catch (error) {
    console.error("Error:", error);
  }

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Support

For feedback, support or questions about Flashblocks, please don’t hesitate to contact us in the #developer-chat channel in the Base Discord.