Imported from maelrx/Zugzwang (.agents/skills/implement-evaluator-metric/SKILL.md). Install upstream with npx skills add maelrx/Zugzwang --skill implement-evaluator-metric. Copyright stays with the author.

Implement evaluator or metric

Workflow

1. State exactly which construct the metric measures: protocol, state, policy, value, trajectory, explanation, cost or human alignment.
2. Define inputs, exclusions, units, aggregation and missingness.
3. Assign stable metric ID and semantic version.
4. Record evaluator software/version/config/budget and dataset slice.
5. Keep post-hoc evaluator outside live decision path unless regime declares assistance.
6. Define cache key over all outcome-relevant inputs.
7. Add fixtures for normal, mate, illegal, missing and extreme cases.
8. Test deterministic recomputation from bundle.
9. Add uncertainty-compatible raw observations; do not persist only aggregate.
10. Document invalid comparisons.

Chess-specific cautions

• ACPL depends on engine, budget and mate normalization;
• top-1 punishes equivalent moves;
• legal rate measures rules/interface, not strength;
• Elo/Glicko belongs to a pool/protocol;
• human move matching is not optimality;
• LLM-as-judge is not the sole fact verifier.