> ## Documentation Index
> Fetch the complete documentation index at: https://docs.base.org/llms.txt
> Use this file to discover all available pages before exploring further.

# pendingLogs

> Subscribe to logs from pre-confirmed transactions matching an optional filter. Only available on Flashblocks WebSocket endpoints.

Subscribe via `eth_subscribe` to receive logs from pre-confirmed transactions matching an optional filter. Useful for monitoring contract events with sub-block latency.

<Info>
  Only available on Flashblocks WebSocket endpoints: `wss://mainnet-preconf.base.org` / `wss://sepolia-preconf.base.org`.
</Info>

<Note>
  Requires [base/base](https://github.com/base/base) minimum client version v0.3.1.
</Note>

<Warning>
  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.
</Warning>

## Parameters

<ParamField body="subscriptionType" type="string" required>
  Must be `"pendingLogs"`.
</ParamField>

<ParamField body="filterOptions" type="object">
  Optional log filter.

  <Expandable title="Filter options">
    <ParamField body="address" type="string | array">
      A single contract address or array of addresses to filter by.
    </ParamField>

    <ParamField body="topics" type="array">
      Array of topic filters in the same format as `eth_getLogs`.
    </ParamField>
  </Expandable>
</ParamField>

## Returns

<ResponseField name="result" type="string">
  Hex-encoded subscription ID.
</ResponseField>

## Example

<CodeGroup>
  ```json Subscribe (with filter) theme={null}
  {
    "jsonrpc": "2.0",
    "id": 1,
    "method": "eth_subscribe",
    "params": [
      "pendingLogs",
      {
        "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
        "topics": ["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"]
      }
    ]
  }
  ```

  ```json Subscription ID Response theme={null}
  {"jsonrpc": "2.0", "id": 1, "result": "0x2a7bc8d4e3f5a6b1c2d3e4f5a6b7c8d9"}
  ```
</CodeGroup>