There is a quiet failure mode with AI agent skills that almost everyone hits: you build a custom skill, it looks perfect, and it simply never runs. No error, no warning. It just sits there unused. The reason is remarkably consistent, and so is the fix.
The failure is silent
Unlike a bug that throws an error, a skill that never triggers gives you nothing to debug. You ask for the thing the skill was built for, the agent does something reasonable without it, and you never realize the skill was skipped. That silence is what makes this so common — people do not even know it is happening.
The cause is almost always the description
An agent chooses which skills to use by reading their descriptions and matching them against your request. If the description does not match how you phrased things, the skill is skipped. And most descriptions are written too narrowly — as a label for the task rather than a map of how people ask for it.
"Reviews pull requests" is a label. But you do not always say "pull request." You say "check this," "look this over," "audit my code." None of those match, so the skill never fires.
The one fix
Write the description around the language you actually use, and list the synonyms:
description: Reviews code for bugs, style and security. Use when
the user asks to review, check, audit or look over code, a pull
request, a diff, or a specific file.
This matches nearly any natural phrasing of the request. It is the single highest-leverage change you can make to a skill, and it fixes the large majority of "my skill does not work" cases.
How to confirm it is fixed
Test the way you actually talk. Phrase a few casual, natural requests — the way you would on a busy afternoon — and watch whether the skill loads. If a reasonable request misses, add those exact words to the description and try again. A couple of rounds and it fires every time.
Prevent it from the start
The habit that prevents the silent failure entirely: write the description first, before the body, around real phrasing. It forces you to think about when the skill should fire before you think about what it does. Get the trigger right, and all the careful work inside the skill finally gets used.
The bottom line
Most custom skills do not fail because they are badly written. They fail because they are never triggered, and that comes down to one field. Write descriptions around how you actually ask, test with natural phrasing, and your skills stop gathering dust.
Free starter: The format, a working template, and the description technique are all on a free cheat sheet: AI Agent Skills Quick-Start Cheat Sheet
Go deeper: The full guide covers the complete specification, five build walkthroughs, ten production-ready templates, security, and a 30-day plan: AI Agent Skills: The Complete SKILL.md Standard Guide
What is your experience — have your custom skills been firing reliably, or silently sitting unused? Curious to compare notes below.
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