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.

This subscription requires a WebSocket-enabled RPC endpoint. The public Base endpoints (mainnet.base.org, sepolia.base.org) are HTTP only. Choose a Flashblocks-capable WebSocket provider from the Base Services Hub.

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.

Parameters

subscriptionType · string · required

Must be "pendingLogs".

filterOptions · object

Optional log filter.

Show Filter Options

address · string | array

A single contract address or array of addresses to filter by.

topics · array

Array of topic filters in the same format as eth_getLogs.

Returns

result · string

Hex-encoded subscription ID.

Example

Subscribe (with filter)

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