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

# count()

**Signature:** `count(<condition>, "<time_window>")`

**Parameters:**

| Parameter     | Type                       | Description                                               |
| ------------- | -------------------------- | --------------------------------------------------------- |
| `condition`   | Conditional Expression     | A `when` clause that filters which transactions to count. |
| `time_window` | String (ISO 8601 Duration) | The lookback period (e.g., `"PT24H"` for 24 hours).       |

**Return Value:** An integer representing the number of matching transactions within the time window.

**Description:** Counts the number of historical transactions that match the given filter condition within the specified time window. The count is then compared against a threshold using a standard comparison operator.

**Example: High Frequency Detection**

```shellscript lines theme={null}
rule HighFrequencyDestination {
    description "Unusually frequent payments to the same destination may require scrutiny."

    when count(when destination == $current.destination, "PT24H") > 10
     and amount > 100

    then review
         score   0.5
         reason  "High frequency of transactions to same destination in 24 hours"
}
```

**How it works internally:** The engine translates this into a SQL query against DuckDB:

```sql lines theme={null}
SELECT COUNT(*) FROM transactions
WHERE destination = '<current transaction destination>'
AND timestamp >= '<now - 24 hours>'
```