Deprecate

Code is a liability, not an asset. Every line carries ongoing cost: tests, docs, security patches, dependency updates, mental overhead. Deprecation is the discipline of removing code that no longer earns its keep. Migration is the process of moving users safely from the old to the new.

Most teams build well, few remove well. This skill addresses the gap.

Core Principles

Code is a liability

Functionality has value; code has cost. When the same functionality can be provided with less code or better abstractions, the old code should go.

Hyrum's Law makes removal hard

With enough users, every observable behavior becomes depended on — including bugs, timing quirks, and undocumented side effects. Deprecation requires active migration, not just announcement. Users can't "just switch" when they depend on behaviors the replacement doesn't replicate.

Plan deprecation at design time

When building something new, ask: "How would we remove this in 3 years?" Clean interfaces, feature flags, and minimal surface area are easier to deprecate.