A local rule runs in-process inside Specter – boolean conditions, velocity counters, and checks over enriched metadata. It evaluates in microseconds, needs no external call, and carries no per-decision fee. A backend rule delegates scoring to an external risk engine (such as Worldpay FraudSight) reached through a Link integration, for judgements a single transaction can't make on its own.

The rule of thumb: deterministic and cheap belongs local; probabilistic or dependent on data you don't hold belongs in a backend. Most fraud is caught by the cheap local net, so the paid model call is reserved for genuinely ambiguous transactions.

→ See how Specter's rule engine works