Variables - FinWatch

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:

$sanctioned_countries
$high_risk_bins
$blocked_accounts

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

$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:

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:

// "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

​Purpose

​Syntax

​Usage with the in Operator

​The $current Variable

​Variable Naming Conventions

Purpose

Syntax

Usage with the `in` Operator

The `$current` Variable

Variable Naming Conventions