Three NestJS Architecture Tips for Building Scalable Fraud Detection Systems

A software developer has outlined common structural pitfalls NestJS developers encounter when building banking fraud detection logic. The core problem arises when multiple fraud rules are stacked inside a single validation method, making the codebase fragile and difficult to maintain over time. The recommended fix is to give each fraud rule its own isolated class that implements a shared interface, ensuring bugs in one rule cannot affect others. A central service then loops through all available rule classes dynamically, eliminating the need to modify core logic whenever a new rule is introduced. This open-closed design pattern allows teams to scale fraud detection by simply adding new rule classes without touching the existing engine.