The majority of skills I see teams define for their coding agents are just re-teaching the LLM things it already knows.
Test-driven development. Hundreds of tokens explaining what TDD is, how to write a failing test first, then make it pass, then refactor. Paragraphs of carefully crafted instructions.
You know what works just as well?
"Build with test-driven development."
That's it. One sentence. The model already knows TDD. What it doesn't know is your codebase — where your tests live, what conventions you've settled on, what frameworks you're using. It'll figure that out by reading your files. Let it.
The instinct to over-specify everything comes from a good place. You want consistency across teams, across repos, across the org. But here's the problem: the more you try to force uniformity through skills, the less you get out of your agents. Every project has nuance. Every codebase has corner cases. Rigid, opinionated skills don't accommodate that — they just get in the way.
And let's be honest about something: the codebases we humans wrote before agentic coding weren't perfect either. We're not protecting some pristine standard. We're projecting our preferences onto tools that, in 2026, are genuinely good at the craft.
Your customers don't care if your tests live in __tests__ or spec/. They don't see your folder structure. They don't know if you're on pnpm or npm. Those are not business outcomes.
So what ARE skills actually good for?
Organizational knowledge. The stuff the model has no way of knowing and can't figure out by reading your repo.
Things like: your AWS account has a Service Control Policy that blocks certain infrastructure deployments. Without that in a skill, your agent will attempt the deployment, fail, speculate about why, try a few more approaches, and eventually — after 20,000 burned tokens — figure out it was the SCP all along.
That's the pattern. Hard blockers. Guardrails that aren't visible in the code. Internal constraints that exist outside the repository. That's what skills are for.
If your agent would hit a wall and have no way to reason its way out, document it.
If your agent already knows how to do it — get out of the way.