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Claude decides whether to load a skill based on a single-line description…

2026-05-13 · 01:00 UTC ·@aakashgupta ·1 min read

Brief

Author @aakashgupta (2026-05-13) shows that Claude's routing relies on a single-line skill description, causing sub-100-character descriptions to be invisible. He audited 25 skills (75 runs), fixed a failing recipe skill by rewriting its description with explicit triggers and boundaries, and provides a six-rule post-load checklist plus an eval prompt and audit kit for reliable skill design.

Why it matters

Claude decides whether to load a skill based on a single-line description; descriptions under 100 characters often remain invisible. In tests of 25 skills across 75 runs, a recipe-planner with a 37-character description ("Suggest recipes from what's in fridge.") failed to trigger for most of 10 prompts until its description was rewritten with 3 real-user trigger phrases, third-person voice, and an explicit "do not use X / use /Y instead" boundary.

Key details

  • After routing, follow six post-load rules: (1) write commands, not requests (e.g., "Flag every issue with severity Critical/High/Medium/Low" beats "could you take a look"), (2) provide a read-first 3-column table (Source, Path, What to extract), (3) include one worked input/output example, (4) keep skills under 500 lines (safety rules at line 700 never fire), and (5) pair every "do not use for X" with a "use /Y instead" pointer. A full audit checklist and a 10-sub-agent eval prompt are available at aibyaakash.com/p/claude-skil….
Source evidence

Most people's Claude Skills are invisible to Claude.

Claude scans every installed skill's description before deciding to load it. The decision happens from that single line. Skills with descriptions under 100 characters stay invisible because Claude can't tell what they do.

I tested 25 of my top Skills across 75 runs last week. The recipe planner I built had a 37-character description: "Suggest recipes from what's in fridge." I sent 10 prompts that should have triggered it. "What can I make tonight." "I don't want to go grocery shopping." "Help me use up what's in my fridge." Most missed.

Rewrote the description with 3 trigger phrases a user would actually type, third-person voice, and one "do not use for X, use /Y instead" boundary. Same skill. Now those prompts fire.

That's the routing layer. The other 6 laws are about what happens after the skill loads:

  • Write commands, not requests. "Flag every issue with severity Critical/High/Medium/Low" beats "could you take a look."
  • Build a read-first table with Source, Path, What to extract. The 3-column structure tells Claude which directory to search, what terms to look for, what to pull out.
  • Include a worked input/output example. One example beats 12 rules.
  • Keep skills under 500 lines. Safety rules buried at line 700 of a fitness skill never fire.
  • Every "do not use for X" needs a "use /Y instead" pointer.

Full audit checklist plus an eval prompt that runs 10 sub-agents against your skill is in the deep dive:

aibyaakash.com/p/claude-skil…

Skills are the new prompts. Most people are still writing them like 2023 prompts.