Dependency fan-out

What it means

Dependency fan-out measures outward dependency links from a module, service, or package. High fan-out can increase setup complexity, failure propagation, and the amount of external behavior a component must understand. It can also be appropriate for an orchestration layer. The signal becomes meaningful when compared with ownership boundaries, change frequency, and failure isolation.

Example

An API handler imports seven adapters, three policy modules, and several infrastructure clients. A review of its fan-out reveals that business decisions and transport concerns are mixed, suggesting a narrower application service boundary.

Limitations

Fan-out counts do not capture dependency quality, call frequency, or whether edges are optional. A small number of critical dependencies can be more dangerous than many well-isolated ones. Avoid setting a universal threshold without local evidence.

How to use the signal

Weave can help correlate fan-out-heavy changes with review duration and rework. Use the architecture analyzer to calculate the measure, then inspect actual pull requests and incidents before choosing a refactoring priority.