Building Good Skills

Day 3

Skills package a capability so it can be invoked reliably and reused. Day 3 is about what separates a good skill from a brittle one — and how to build them.

What makes a skill good

• Clear scope: it does one thing, and its boundaries are obvious.
• Reliable: it behaves predictably across inputs, not just the happy path.
• Reusable: it can be dropped into different contexts without rework.
• Legible: someone else (or future you) can understand and trust it.

Building skills

• Designing the interface: inputs, outputs, and failure behavior.
• Writing the instructions and context the skill needs to succeed.
• Testing a skill against realistic inputs, including adversarial ones.

Quality over slop

A good skill is a concrete antidote to AI slop: it encodes a validated way of doing something, so you're not re-deriving quality from scratch every time.

Outcomes

You should leave able to build and use Claude Code skills, and to tell a well-engineered skill from one that only appears to work.