This article shows that SKILL.md files aren’t static prompts but loader specifications defining what to load, when, and at what cost. It breaks down the three progressive-disclosure levels, explains how architecture—not instruction content—drives context consumption, and highlights common antipatterns that bloat or break skills.

• A 1,200-line monolithic SKILL.md ate 20% of the context window every turn; splitting it into a 180-line driver plus reference files and a script dropped that to 7%.
• SKILL.md files are loader specs with three tiers—frontmatter (~100 tokens, always loaded), body (loads on invocation, keep under 500 lines), and references/scripts (loaded or run only on demand).
• Adding YAML frontmatter to reference files accidentally promotes them to always-loaded skills, cluttering the skill list and causing out-of-context invocations—removing it fixed silent routing errors.
• Context consumption is driven by how content is architected across these layers, not by how much instructional detail is written.