newFlashblockTransactions

Subscribe to receive each transaction as it is pre-confirmed into a Flashblock. Only available on Flashblocks WebSocket endpoints.

Subscribe via eth_subscribe to receive each transaction as it is pre-confirmed into a Flashblock. Pass true as the second parameter to receive full transaction and receipt data.

This subscription requires a WebSocket-enabled RPC endpoint. The public Base endpoints (mainnet.base.org, sepolia.base.org) are HTTP only. Use a node provider such as Alchemy or QuickNode that offers WebSocket support for Base.

Requires base/base minimum client version v0.8.0.

Each subscription emits one item per WebSocket message. Events arrive approximately every 200ms. If your handler performs heavy processing per event, throttle or debounce it to avoid blocking.

Parameters

subscriptionType · string · required

Must be "newFlashblockTransactions".

full · boolean

If true, each notification includes the full transaction object with receipt fields embedded. Defaults to false (transaction hash only).

Returns

result · string

Hex-encoded subscription ID returned on subscribe.

Notifications

Each notification is a standard eth_subscription message. The params.result field depends on the full parameter:

full: false — result is the transaction hash:

"0xe26de91f9037e903eefe70b28f613019253da603e67e0dbfe2f656dce5444311"

full: true — result is a transaction object with receipt fields embedded directly (no nested receipt sub-object). Verified live against base/v0.9.0:

type · string

Transaction type: 0x0 Legacy, 0x2 EIP-1559, 0x7e Deposit.

chainId · string

Chain ID (hex).

nonce · string

Sender nonce (hex).

gas · string

Gas limit (hex).

maxFeePerGas · string

EIP-1559 max fee per gas (hex).

maxPriorityFeePerGas · string

EIP-1559 max priority fee per gas (hex).

to · string

Recipient address.

value · string

ETH value transferred (hex).

accessList · array

EIP-2930 access list.

input · string

Transaction input data (hex).

r · string

Signature r component.

s · string

Signature s component.

yParity · string

Signature parity (hex).

v · string

Signature v value (hex).

hash · string

Transaction hash.

blockHash · null

Always null — transaction is pre-confirmed, not yet in a finalized block.

blockNumber · string

Block number (hex) of the in-progress Flashblock.

transactionIndex · string

Index within the block (hex).

from · string

Sender address.

gasPrice · string

Effective gas price (hex).

gasUsed · string

Gas used by this transaction (hex). Note: changed from integer to hex string in v0.8.0.

status · string

0x1 for success, 0x0 for failure.

cumulativeGasUsed · string

Total gas used in the block up to and including this transaction (hex).

contractAddress · string | null

Address of the created contract, or null.

logsBloom · string

Bloom filter of logs (hex).

logs · array

Array of log objects emitted by this transaction.

gasUsed is a hex string (e.g. "0x26132"), not an integer. This changed in v0.8.0 — update any parsers that expect a numeric value.

Example

Subscribe

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

{"jsonrpc": "2.0", "id": 1, "method": "eth_subscribe", "params": ["newFlashblockTransactions", true]}

{"jsonrpc": "2.0", "id": 1, "result": "0x1887ec8b9589ccad00000000000532da"}

{
  "jsonrpc": "2.0",
  "method": "eth_subscription",
  "params": {
    "subscription": "0x1887ec8b9589ccad00000000000532da",
    "result": "0xe26de91f9037e903eefe70b28f613019253da603e67e0dbfe2f656dce5444311"
  }
}

{
  "jsonrpc": "2.0",
  "method": "eth_subscription",
  "params": {
    "subscription": "0x1887ec8b9589ccad00000000000532da",
    "result": {
      "type": "0x2",
      "chainId": "0x2105",
      "nonce": "0x34ed",
      "gas": "0x7a1200",
      "maxFeePerGas": "0x257ab3c",
      "maxPriorityFeePerGas": "0x419c7c",
      "to": "0x6211a3742cf9d3b6677ecc7fd9dd102ab101d8e2",
      "value": "0x0",
      "accessList": [],
      "input": "0x...",
      "r": "0xa7cd30d21c30d4d60d27073c8bbc3ef5778527cf98eae0433e9d1f18c929dd5d",
      "s": "0x08c75921e6bb75e19112300f80998f88a2b0f1adc52df2c3597b171d8c8de68d",
      "yParity": "0x1",
      "v": "0x1",
      "hash": "0x6a010a5ce041ff0ee5a926db65d1ef512836cae822d5f2d58b63981bfa40aa7f",
      "blockHash": null,
      "blockNumber": "0x2c679a1",
      "transactionIndex": "0x83",
      "from": "0x2ad149d3d3099532d7c25c47cce37db6c4677b3a",
      "gasPrice": "0x8de7bc",
      "gasUsed": "0x26132",
      "status": "0x1",
      "cumulativeGasUsed": "0x16cb406",
      "contractAddress": null,
      "logsBloom": "0x00...00",
      "logs": []
    }
  }
}