Crafting Instructions for Claude

Choose the format for instructions on Claude.ai — Project instructions, Skills, or standalone prompts — and structure them for the format chosen.

Overlap notice. The Core Optimization Principles below also appear in writing-instructions, which carries them in more depth alongside model-aware calibration, complexity scaling and a quality checklist. The two skills were written independently and never reconciled; a 2026-08-24 retrieval measurement put their descriptions at 0.843 cosine, the most confusable pair in the 92-skill catalogue. Until they are merged, this skill owns the format decision and writing-instructions owns how to write well inside a format.

Decision Framework: Which Format to Use?

Ask these questions to determine the right format: