> ## 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.

# Variables

Variables allow you to inject dynamic, externally-managed data into your rules without modifying the rule's source code.

### Purpose

Variables solve a critical operational problem: some data changes more frequently than the rules that reference it. For example:

* A **sanctioned countries list** is updated quarterly by OFAC.
* A **list of known fraud BINs** changes daily.
* A **high-risk MCC list** is managed by a compliance team.

Without variables, every update to these lists would require a code change, a PR, and a deployment. With variables, the list is managed externally and the rule remains static.

### Syntax

Variables are referenced using the `$` prefix:

```ws theme={null}
$sanctioned_countries
$high_risk_bins
$blocked_accounts
```

Variables also support **dot notation** for accessing properties of the current transaction context:

```ws theme={null}
$current.source        // The 'source' field of the current transaction
$current.destination   // The 'destination' field of the current transaction
$current.amount        // The 'amount' field of the current transaction
```

### Usage with the `in` Operator

The most common use case is checking a field against a variable list:

```ws theme={null}
rule SanctionedCountryCheck {
    description "Blocks transactions to sanctioned countries."

    when metadata.destination_country in $sanctioned_countries

    then block
         score   1.0
         reason  "Destination country is on global sanctions list"
}
```

### The `$current` Variable

The special `$current` variable provides access to the transaction currently being evaluated. It is used **inside function arguments** to create self-referencing filters:

```ws theme={null}
// "Count transactions where the destination matches THIS transaction's destination"
count(when destination == $current.destination, "PT24H")

// "Sum amounts where the source matches THIS transaction's source"
sum(when source == $current.source, "PT24H")
```

**How it works:** At runtime, `$current.source` is resolved by the interpreter using the `resolvePlaceholder` function. It looks up the field path in the current transaction's data and substitutes the actual value. If the field does not exist, the condition evaluates to `false`.

### Variable Naming Conventions

* Use `snake_case` prefixed with `$`.
* The name should clearly describe the content of the variable.
* Good: `$sanctioned_countries`, `$high_risk_mccs`, `$blocked_card_bins`
* Bad: `$list1`, `$data`, `$x`