How to Make a SKILL.md

Everything you need to know about crafting effective instructions that make Claude work exactly the way you want.

What is a SKILL.md?

A SKILL.md is a plain text file written in Markdown that contains system prompts, rules, and guidelines for Claude. By uploading a SKILL.md to your Claude project, you effectively teach Claude a new "skill"—changing its default behavior, tone, and output format for that specific project.

Think of it as programming Claude with natural language. Instead of repeatedly telling Claude how to format code, write emails, or analyze data in every single prompt, you define it once in a SKILL.md.

Anatomy of a Good Skill

The most effective skills follow a structured format. We recommend using clear headings to separate the AI's identity, rules, and output format.

Mission/Identity: Tell Claude exactly who it is and what its primary goal is.
Rules: Provide a numbered list of strict constraints. Negative constraints ("NEVER do X") are often more effective than positive ones.
Format: Specify exactly how you want the output to look.

The Golden Rules

1
Be specific, not vague.Instead of "write well", use "use short sentences, active voice, and an 8th-grade reading level."
2
One job per skill.Don't try to make a skill that writes code AND writes marketing copy. Split them into two separate skills.
3
Test before uploading.Always test your prompt in Claude before sharing it here to ensure it actually behaves the way you expect.

Full Working Example

Here is an example of a simple but highly effective email response skill. Notice how it uses clear sections and strict rules.

SKILL.md

markdown

---
name: Email Responder Pro
description: Drafts professional and concise email replies based on rough notes.
---

# MISSION
You are an expert executive assistant. Your job is to take rough, bulleted notes from the user and turn them into polished, professional, and concise email replies.

# RULES
1. NEVER use the words "delve", "testament", or "tapestry".
2. Keep the email under 150 words unless specifically requested.
3. Always adopt a polite but firm tone.
4. If the user's notes are angry, soften the tone to remain professional.

# FORMAT
Output ONLY the email body. Do not include subject lines or placeholder brackets like [Your Name] unless explicitly told to.

Common Mistakes

Being too polite: You don't need to say "please" to the AI in a system prompt. Be direct and commanding.
Contradictory rules: Ensure Rule 2 doesn't accidentally cancel out Rule 5. Keep it simple.
Bloat: Providing 5 pages of instructions usually degrades performance. The best skills are concise.

Ready to share your skill?

Upload your SKILL.md to the Vault and help other Claude users upgrade their workflows.