Course B · Module B2 Going Agentic · Lesson 15 of 18

Build Your Own Skill or MCP Server deep dive

Package your own expertise so any agent can use it.

~20 min · Have your project folder open · Prereq: B14 (Open Source)

At the very start of this course you ran npx skills add and installed the mattpocock teach skill — a folder of instructions that gave your AI a new capability with a single command. You used someone else's packaged expertise. This lesson's single win is understanding how to package your expertise the same way — so any agent on your machine (or your team's) can tap into it. By the end you'll know the shape of a skill, when to build one versus something heavier called an MCP server, and you'll have a clear path to building your first one.

A skill is just a folder with instructions

Remember the teach skill you installed? Under the hood it's a folder containing a file called SKILL.md — plain text that tells the AI what the skill does, how to invoke it, and what steps to follow. That's it. No compilation, no deployment, no infrastructure.

Think of it as a saved prompt with a name and a trigger. You give it a name like /onboard-client, write out the steps you follow every time you onboard a new client, and from that point on any agent session can run your exact process just by invoking the skill name.

The anatomy of a skill

A skill lives in a .claude/skills/your-skill-name/ folder. At minimum it needs one file:

SKILL.mdA plain-English description of the skill: what it does, when to use it, and step-by-step instructions the agent follows.

README.md (optional)Human-readable docs for you or your team — what the skill does, how to invoke it, any prerequisites.

templates/ (optional)Any example files, prompt snippets, or output samples the skill references during its steps.

Here is a minimal SKILL.md for a fictional "weekly-report" skill — just to show you the shape:

# weekly-report skill

## What this does
Generates a formatted weekly progress report from bullet notes.

## When to use it
Run /weekly-report at the end of each work week.

## Steps
1. Ask the user to paste their raw bullet notes for the week.
2. Organise into: Wins / Blockers / Next-week priorities.
3. Write in plain, confident language — no jargon.
4. Output as a ready-to-paste email.

That's the whole thing. When you run /weekly-report in a Claude session, the agent reads those instructions and follows them. Your expertise is now reusable — by you, your VA, or any collaborator with access to the folder.

Skill vs MCP server — when to build which

A skill is the right tool when you want to package reusable instructions or a multi-step process. But sometimes your agent needs to reach out and talk to a live system — read from your database, query an API in real time, trigger an action in your CRM. That's where an MCP server comes in.

Build a skill when…

You want to save a repeatable prompt or process
The expertise lives in your head (or your team's)
No live data connection needed
Example: onboarding checklist, report template, review process

Build an MCP server when…

Your agent needs to read/write a live data source
You're connecting to an API that doesn't have a built-in tool
You need real-time information inside the agent session
Example: query your own database, push to your CRM, read live sensor data

MCP stands for Model Context Protocol — an open standard that defines how an agent talks to external tools. An MCP server is a small program that sits between your agent and some data source or API, translating requests both ways. The quickstart guide (linked below) shows the simplest possible version in about 50 lines of code — well within reach with AI assistance.

Start with a skill, not an MCP server. A skill costs you 20 minutes and a text file. An MCP server costs you a few hours and a bit of code. Most reusable expertise you have right now belongs in a skill. You'll know you've hit the limit when the agent keeps asking you to paste in data you wish it could just fetch itself — that's the moment to graduate to MCP.

You are closer than you think

Every repeatable process you follow in your business — your client intake, your content calendar, your product launch checklist — is exactly the material skills are made of. You've been building this expertise for years. Packaging it takes an afternoon. Once it's packaged, any agent session, any team member, any future hire can run your proven process with a single command.

That's the genuine superpower here: you stop being the bottleneck on your own expertise. The knowledge travels with the project folder, not just with you. It's one of the most worthwhile things you can build.

Check yourself

Answer before opening. Recalling it now is what makes it stick.

What is the minimum file needed to create a skill, and where does it live?

A SKILL.md file inside a folder named after your skill under .claude/skills/. It contains a plain-English description of what the skill does and the steps the agent should follow.

Your agent needs to pull live order data from your Shopify store during a session. Skill or MCP server?

MCP server. A skill packages instructions — it can't make live API calls on its own. An MCP server acts as the bridge between the agent and a live data source like Shopify's API.

You have a 7-step onboarding process you follow with every new client. Is this skill material?

Absolutely yes. A repeatable process made of instructions is exactly what skills are for. Write out the 7 steps in a SKILL.md, name the skill /onboard-client, and you can run your exact process from any agent session, and so can anyone on your team.