poka-yoke

Poka-Yoke: Mistake-Proofing for Software

Shigeo Shingo's insight, from the Toyota Production System: people will always make mistakes; that is not the problem worth solving. The problem is letting a mistake become a defect. So you stop trying to make humans more careful and start redesigning the work so the mistake either cannot physically happen or announces itself immediately.

A poka-yoke ("poh-kah yoh-kay", ポカヨケ) is a device: a jig, a shape, a counter: not an instruction. In software: a type, a constraint, a hook, a schema, a state machine. The single most important consequence:

**A comment, a docstring, a wiki page, a code review checklist, or a line in CLAUDE.md

saying "don't do X" is not a poka-yoke.** It is training. Training degrades. A device

does not. If your proposed fix relies on someone remembering something, keep going.

When to Use This Skill

• Use when the user says "poka-yoke this", "mistake-proof it", or "make this harder to get wrong".
• Use when designing an interface, schema or state machine and the ask is "make invalid states unrepresentable" or "so callers cannot screw it up".
• Use when auditing existing code for footguns: "what could bite us here", "what is easy to misuse".
• Use after an incident, when the fix must close the class rather than the case: "make sure this never happens again", "this is the third time".
• Especially fo