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Subscribe via eth_subscribe to receive logs from pre-confirmed transactions matching an optional filter. Useful for monitoring contract events with sub-block latency.
Only available on Flashblocks WebSocket endpoints: wss://mainnet-preconf.base.org / wss://sepolia-preconf.base.org.
Requires base/base minimum client version v0.3.1.
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.

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Parameters

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subscriptionType
string
required
Must be "pendingLogs".
​
filterOptions
object
Optional log filter.

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Returns

​
result
string
Hex-encoded subscription ID.

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Example

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "eth_subscribe",
  "params": [
    "pendingLogs",
    {
      "address": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "topics": ["0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"]
    }
  ]
}