clean-architecture

Start with use cases written in business language, identify entities and their rules, then sketch interactors with input/output DTOs and ports. Defer database and framework decisions, and organize directories by business component rather than by layer.

Break cycles using the Acyclic Dependencies Principle: either apply dependency inversion by introducing an interface in the more stable component, or extract a third component both sides depend on. Add cycle detection to CI to prevent recurrence.

Start with source-level decoupling inside a well-structured monolith. Promote individual boundaries to deployment units, processes, or services only when operational pressure justifies it, since tightly coupled services are worse than a clean monolith.

Yes, the principles are language-agnostic. The skill includes enforcement tooling per ecosystem, such as import-linter for Python, dependency-cruiser and madge for JavaScript, ArchUnit for Java, and cargo-modules for Rust.

Establish a test safety net first, triage hotspots by change frequency, then draw a seam around the worst module using a Facade or Strategy interface. Add characterization tests at the seam and refactor incrementally inside it, one hotspot at a time.

I measures instability as fan-out over total coupling, A measures abstractness as abstract types over total types, and D measures distance from the ideal Main Sequence as |A+I−1|. Components with D above 0.1 are drifting toward the Zone of Pain or Zone of Uselessness.