How Skills Work
10 min readA skill is a job description you hand Claude once and invoke whenever you need it. Here's what they are, the built-ins you already have, and how the skills you unlock on the SkillTree map plug in.
What is a skill?
A skill is a reusable instruction set stored in a SKILL.md file. When you invoke a skill with a slash command, Claude loads those instructions and follows a specific, consistent workflow · instead of improvising from scratch every time.
Think of it like giving Claude a job description for a specific task. Rather than re-explaining what you want, you install the skill once and invoke it when needed. This is exactly what an "AI employee" on the SkillTree map is · a skill file that does one real job in your business: sales research, client reporting, invoice processing, CRM updates, onboarding.
Skills come from three places:
- Built-in · ship with Claude Code, no setup required
- SkillTree · the 79 runnable skill files you unlock on the map, each one an AI employee you install into your own Claude Code with a single command
- Custom · skills you write yourself for a workflow specific to you
The built-in skills you should know
Type /skills in Claude Code to see everything available. The most useful built-ins:
| Skill | What it does | When to use it |
|---|---|---|
/review | Reviews code or writing for quality · spawns parallel agents | After finishing any piece of work |
/simplify | Cleans up recently changed files for efficiency and reuse | After a larger build or refactor |
/debug | Systematic debugging with root-cause analysis | When something breaks and you don't know why |
/loop | Runs a task repeatedly until a condition is met | For monitoring, polling, or iterative refinement |
/batch | Runs the same task across multiple inputs in parallel | When you have the same job across many files or items |
Most people don't know these exist. Try /review on anything you've just written · code, an email draft, a document. You'll get a structured critique in about thirty seconds. It's the fastest way to feel what a skill does before you install one from the map.
Key commands to know
Beyond skills, these slash commands save you time daily:
| Command | What it does |
|---|---|
/skills | List all available skills |
/compact | Compress conversation history to free up context · do this at ~50% full |
/clear | Start a fresh session · use when switching to a new task |
/diff | Show all changes Claude has made in the current session |
/config | Set your preferred response style (Explanatory, Concise, or Technical) |
/init | Generate a starter CLAUDE.md for your current project |
/voice | Enable push-to-talk · hold Space to dictate |
Installing a skill from the SkillTree map
The skills you unlock on the map install the same way · each one is a SKILL.md file that drops into your project (or ~/.claude/skills/ for a global skill) and becomes invokable by name. Open the skill on the map, follow its install command, and it's live in your next session. From there you invoke it like any built-in.
The point of the map is that you're not writing every one of these from scratch. You browse the jobs across the seven departments of a business, find the AI employee that does the job you're sick of doing, and install it. Each one already reads from your brain, so it shows up knowing your business.
Writing your own
When no skill exists for a job you do often, you write one. A skill is just a SKILL.md file with a name, a description of when to use it, and the steps Claude should follow. Start by doing the task manually with Claude a few times, then ask Claude to turn that workflow into a skill file. That's the whole loop · do it once well, capture it, never explain it again.