Implexa

What Are Claude Skills? (5-Minute Explainer)

A Claude Skill is a reusable instruction pack — a small directory with a SKILL.md file inside — that Claude loads on demand when a matching task comes up.

Instead of pasting the same multi-paragraph prompt every time you want to do something repeatable, you write the instructions once as a skill. Claude figures out when to use it.

This page is the short version: what a skill is, what's inside it, how it compares to a prompt, and where to go next.

The one-sentence version

A Claude Skill is a function Claude knows how to call — defined in plain Markdown, loaded automatically when its description matches the user's request.

What's inside a skill

Every skill is a directory. The only required file is SKILL.md:

prep-sales-call/
└── SKILL.md

SKILL.md has YAML frontmatter at the top, then Markdown:

---
name: prep-sales-call
description: Prep for a sales call — pull CRM activity, recent news,
             and the last touchpoint for the named account.
---

# Sales call prep

## When to use
When the user mentions an upcoming meeting with a named company.

## Inputs
- Company name or domain
- Meeting date (defaults to next 7 days)

## Procedure
1. Call `crm_query` for the account
2. Pull last 5 activities across all contacts
3. Call `news_search` for the company, last 30 days
4. Format using the output template below

## Output
**Account:** {name}
**Last touch:** {date, channel, who}
**Recent news:** {3 bullets}
**Recommended angle:** {one sentence}

That's it. No build step, no compile, no install. Drop it in ~/.claude/skills/ and Claude picks it up on next launch.

The 6 components of a good skill

The skill above hits four of the six components that separate skills that work from skills that drift. The full list:

#ComponentWhat it is
1IntentWhy this skill exists and when to trigger it
2InputsWhat the user provides; what defaults apply
3ProcedureThe step-by-step, including specific tools to call
4Decision pointsThe branches — why path A over B when the input varies
5Output contractWhat the result looks like (format, fields, length)
6Outcome signalHow you know it worked next time (CRM event, reply, etc.)

Most skills you'll find online cover 1, 2, 3, and 5. The two that consistently get skipped are decision points and outcome signal — and those are exactly the two that matter when inputs shift or when you want to know if the skill is actually paying off.

Full breakdown in the pillar guide.

Claude Skill vs. prompt

PromptClaude Skill
Reusable?Copy-paste each timeTriggers automatically
Consistent output?Drifts every time you editSame format every run
Shareable?Paste in Slack, hope they save itOne link, anyone runs it
Calls tools?Only what's in current contextSpecifies tools by name
Tracks outcomes?NoYes (with the right skill graph)
Edits over time?Find-and-replace in your NotesRe-record or edit the .md file

A prompt is fine for a one-off. A skill is what you build the second time you find yourself pasting the same prompt.

Where skills live

Two locations, both auto-discovered:

  • ~/.claude/skills/ — user-level. Only you can run them.
  • .claude/skills/ — project-level (inside a repo). Anyone who clones the repo gets them.

If you want a third option — share with your team without giving them repo access, or with the public — you need a skill-graph host like Implexa. It gives each skill a shareable link and tracks outcomes when teammates run it.

How skills get triggered

When you make a request, Claude scans the description fields of available skills. If one matches semantically, Claude loads that skill's SKILL.md and follows the procedure.

The description is the most important line in the whole file. Vague descriptions don't trigger. Specific descriptions trigger reliably. "Help with sales" — won't fire. "Prep for a sales call — pull CRM activity for the named account" — fires every time.

You can also force a skill explicitly with /skill-name if you want to override the auto-trigger.

"Claude Skills" vs. "Claude Code Skills" vs. "Anthropic Skills" vs. "SKILL.md"

These all refer to the same thing:

  • Claude Skills — the general term
  • Claude Code Skills — using them inside the Claude Code CLI specifically
  • Anthropic Skills — Anthropic's branding when they announced the format
  • SKILL.md — the actual file format

All four phrases point to the same SKILL.md spec.

How do you build one?

Two paths:

Hand-write it. Open a text editor, write the SKILL.md, save it in ~/.claude/skills/your-skill/. Works for short skills. Falls apart at length because you have to articulate decisions you'd normally make on autopilot.

Demonstrate it once. Run Implexa and /implexa:record. Do the workflow normally. Answer 2–4 short interview questions about decisions, output format, and what signals success. The skill gets authored from your actual behavior plus your answers — including the decision rationale most hand-written skills skip.

We call the captured layer decision traces: visible tool calls plus the interview-extracted rationale. Walkthrough in How to Create a Claude Skill.

FAQ

Is a Claude Skill the same as a system prompt?

No. A system prompt applies to every message in a conversation. A skill is loaded only when its description matches a request — and unloaded after. You can have hundreds of skills installed without bloating every conversation.

Do I need to write code to build a skill?

No. SKILL.md is plain Markdown. The procedure describes what tools to call, but Claude does the calling.

Can a skill call other skills?

Yes — a skill's procedure can reference another skill by name. Best practice is to keep skills focused on one workflow and compose them rather than building one mega-skill.

Can I version-control skills?

Yes. Either commit the skill directory to a repo (project-level skills live in .claude/skills/), or use a skill-graph host that handles versioning for you.

Do skills work in Claude Desktop or only in Claude Code?

The SKILL.md auto-loader is a Claude Code feature. Claude Desktop and the Anthropic API don't auto-discover skills the same way — you'd paste contents into a system prompt or wrap the skill in an agent.

What's the relationship between Skills and MCP?

MCP (Model Context Protocol) is the protocol Claude uses to call external tools. Skills are the instructions for when and how to call them. A skill typically uses one or more MCP servers as its execution backend.

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