---
title: "pendingLogs"
description: "Subscribe to logs from pre-confirmed transactions matching an optional address and topics filter, with sub-block latency on Flashblocks endpoints."
source: https://basehub.org/api-reference/flashblocks/pendinglogs/
---
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](https://github.com/base/base) minimum client version v0.3.1.

Each subscription emits one item per WebSocket message, with events arriving roughly every 200ms. If your handler does heavy work per event, throttle or debounce it to avoid blocking.

## Parameters

| Name | Type | Required | Description |
| --- | --- | --- | --- |
| `subscriptionType` | string | Yes | Must be `"pendingLogs"`. |
| `filterOptions` | object | No | Optional log filter. |

The `filterOptions` object accepts:

| Field | Type | Description |
| --- | --- | --- |
| `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

| Field | Type | Description |
| --- | --- | --- |
| `result` | string | Hex-encoded subscription ID. |

## Example

### Subscribe (with filter)

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

### Subscription ID response

```json
{"jsonrpc": "2.0", "id": 1, "result": "0x2a7bc8d4e3f5a6b1c2d3e4f5a6b7c8d9"}
```