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Subscribe via eth_subscribe to receive each transaction as it is pre-confirmed into a Flashblock. Pass true as the second parameter to receive the full transaction object, associated logs, and receipt fields.
Only available on Flashblocks WebSocket endpoints: wss://mainnet-preconf.base.org / wss://sepolia-preconf.base.org.
Requires base/base minimum client version v0.8.0. Receipt fields in full mode were added in 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.
Breaking change in v0.8.0: The gasUsed field changed from an optional integer (null or 123456) to a required hex string ("0x1e240"). Existing consumers of newFlashblockTransactions with full: true must update their parsers before upgrading to v0.8.0.

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Parameters

​
subscriptionType
string
required
Must be "newFlashblockTransactions".
​
full
boolean | object
Controls the notification content. Three modes are supported:
  • false (default) — each notification delivers a transaction hash string.
  • true — each notification delivers the full TransactionWithLogs object (transaction fields + logs + receipt fields).
  • Filter object — pass { "address": "0x...", "topics": [...] } to stream only transactions where at least one emitted log matches the filter. Each matching notification delivers the full TransactionWithLogs object. All logs for the transaction are included, not just the matching ones.
The filter object accepts the same address and topics fields as eth_getLogs.

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Returns

The initial eth_subscribe response returns a hex-encoded subscription ID string. After that, the node pushes one notification per WebSocket message for each pre-confirmed transaction. When full is false (default): each notification’s result is a transaction hash string. When full is true: each notification’s result is a transaction object with the following fields:
​
result
object
The pre-confirmed transaction object. Only present when full is true; otherwise result is a transaction hash string.

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Notification Format

When full is false (default), each notification delivers a transaction hash:
Notification (default)
{
  "jsonrpc": "2.0",
  "method": "eth_subscription",
  "params": {
    "subscription": "0x1887ec8b9589ccad00000000000532da",
    "result": "0xabc123..."
  }
}
When full is true, each notification delivers the full transaction object. Receipt fields (gasUsed, status, cumulativeGasUsed, contractAddress, logsBloom) are included directly on the transaction object — there is no nested receipt sub-object:
Notification (full=true)
{
  "jsonrpc": "2.0",
  "method": "eth_subscription",
  "params": {
    "subscription": "0x4f029cbb4655559c37784ec4f3983914",
    "result": {
      "type": "0x2",
      "chainId": "0x2105",
      "nonce": "0x36f0",
      "gas": "0x26b12",
      "maxFeePerGas": "0x146a608",
      "maxPriorityFeePerGas": "0xf4240",
      "to": "0xda3983e1ea25051b242ec0df4acf18e68d08a212",
      "value": "0x0",
      "accessList": [],
      "input": "0x67243482...",
      "r": "0x82df735d...",
      "s": "0x431fa018...",
      "yParity": "0x1",
      "v": "0x1",
      "hash": "0xb2ce9822...",
      "blockHash": null,
      "blockNumber": "0x27920be",
      "transactionIndex": "0xbe",
      "from": "0x68acbb03...",
      "gasPrice": "0xaae286",
      "gasUsed": "0x1a4b2",
      "status": "0x1",
      "cumulativeGasUsed": "0x8f3a1",
      "contractAddress": null,
      "logsBloom": "0x00200000...",
      "logs": [
        {
          "address": "0xda3983e1ea25051b242ec0df4acf18e68d08a212",
          "topics": ["0xddf252ad..."],
          "data": "0x",
          "blockHash": "0x000...000",
          "blockNumber": "0x27920be",
          "blockTimestamp": "0x697c9e5f",
          "transactionHash": "0xb2ce9822...",
          "transactionIndex": "0xbe",
          "logIndex": "0x2d9",
          "removed": false
        }
      ]
    }
  }
}

​
Example

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