Validation-first development

Define state machines from requirements before implementation. Specifications say what the system MUST do. Encode compile-time properties in types first, then layer state machine modeling for properties types cannot express.

Modern insight (2025): State machines exist on a spectrum from runtime enums to compile-time typestates. Use the strongest mechanism available. XState v5 introduces actor model semantics -- state machines are now first-class concurrent entities, not just enum switches.

See approaches for language-specific state machine mechanisms. See examples for brief state machine patterns per language. See formal-tools for specification and model checking tools.

State Machine Taxonomy (decision guidance)