Creating Claude Skills in Cowork and Claude Code: the guide

Creating Claude Skills: what it is and how to get started

If you use Claude a bit more often, you know the pattern. You ask for a quote and get something usable back, but not in your structure. So you explain how you do it. The week after, you do it again. And the week after that, once more.

There are skills for that. You explain once how something works for you, you put that in a folder, and from that moment on, Claude knows. No prompt that you have to look up and paste every time.

We now run 29 of them in the office, from drawing up invoices to setting up an SEO project. Below is what a skill actually is, how to make one yourself in ten minutes, and what the difference is between a skill that works and one that gathers dust.

In short:

• A skill is a folder containing a single file: SKILL.md. It explains what it does, when Claude should use it, and how you approach it.
• You simply write it in Dutch. There is no code involved, unless you want to yourself.
• Only the name and the description are always loaded. Claude reads the rest only when the task calls for it, so twenty skills cost you nothing.
• It works in Cowork, in the Claude apps and in Claude Code. Only the place where you drop the file differs.
• If you link it to your website or application, Claude actually performs the work there instead of just writing it down.
• Start with something you have explained three times this month. That is almost always the best first skill.

In this article:

• What a skill actually is
• When you make one
• Your first skill in ten minutes
• Where you place it in Cowork, Claude Code and the API
• What distinguishes a good skill from a bad one
• What we do with it ourselves
• Skills on your own website or application
• The mistakes everyone makes
• Where you learn further

What a skill actually is

A skill is a folder with a file in it, and that file is called SKILL.md. At the top are two things: a name and a description. Below that, in plain language, is how you want something to happen.

The most important thing to understand is how Claude handles it. At the start, it only reads the name and description of each skill. Nothing more. Only when you ask something that matches a description does it open the entire file. If you have referred in that skill to a second file containing, for example, your rates, that is only read when it is truly needed.

That sounds like a detail, but it is precisely why skills work and a long system prompt does not. You can have twenty of them without it getting in the way. Claude grabs what it needs and leaves the rest.

The second difference compared to a prompt: you don't need to invoke it. You simply ask for a quote, and Claude sees for itself that there's a skill for that. That only works if your description is correct, and we'll come back to that in a moment.

When you make one

Not every task deserves a skill. The rule of thumb that works well for us: if you are explaining something for the third time, write it down.

Good candidates usually have these characteristics:

• It recurs regularly. A quote, a weekly report, a blog, updating a client file.
• It follows a set procedure. Not necessarily written down, but something you have in your head and colleagues don't.
• The outcome must be consistent. Every quote the same structure, every invoice the same format.
• There are rules in there that you quickly forget. “Always state excluding VAT”, “never publish without a second check”. That sort of thing.

Poor candidates are tasks that you do once, or tasks where every situation is so different that there is no pattern to it. For those, you are better off having a good conversation than following an instruction.

Your first skill in ten minutes

Take something small. We are getting a quote here, but fill in what suits you.

Step 1. Just do the task once with Claude first. Without a skill, just in a conversation. Pay attention to everything you have to explain along the way: our structure, our rates, that we always mention a period of validity. What you explain, that becomes your skill.

Step 2. Ask Claude to turn it into a skill. Literally: “turn this into a skill, using our structure and the rule about VAT.” Claude knows the format and writes it for you. You don't need to memorise the syntax.

Step 3. Throw out what Claude already knows. This is the step most people skip. Explaining what a quotation is, is a waste of space. Only what applies specifically to you belongs in it.

Step 4. This is what the result looks like:

---
name: preparing-a-quote
description: Prepares a quote in accordance with the agency’s standard format and rates.
  Use this when someone requests a quote, price quotation or
  cost estimate for a new project.
---

# Preparing a quotation

## Standard structure
1. Our understanding of the request
2. What we will be delivering, broken down by component
3. What is not included
4. Investment and lead time

## Rules
- Never give a total price without a breakdown
- Always specify a validity period of 30 days
- Amounts exclude VAT, and this must be explicitly stated

Step 5. Test it on a real job. Not based on a made-up example. Ask for a quote for a client who is on the agenda for tomorrow and see if Claude picks up the skill and follows the rules. If it doesn't, it's almost always down to the description.

Where you put it

The content is the same everywhere, only the location varies per environment.

• Claude Cowork and the Claude apps. Put your folder in a zip file, with the folder still around it, and upload it under Customize and then Skills. Then just turn it on. Make sure that the folder name is the same as the name in your file.
• Claude Code. No zip file is required here. Put the folder into ~/.claude/skills/ And done. We keep that folder in a shared Drive folder with a shortcut to it, so we have the same skills on two laptops.
• The API. There it works via the code execution tool.

For all three, code execution needs to be turned on. Skills work on the free version and on all paid subscriptions.

Another handy one: in Cowork on the Mac you can skill record. You turn on the recording, demonstrate the task once, and Claude writes a skill from it itself. That takes up to about ten minutes and works on Pro, Max and Team. For people who prefer demonstrating something rather than writing it down, that is the shortest route.

What distinguishes a good skill from a bad one

The difference is almost never in the content. It is in the description and in the length.

A good description is half the battle. That is the only thing Claude sees when it has to choose. So, state what the skill does AND when you use it, and write it in the third person. ‘Draws up a quotation according to the fixed structure. Use this when someone asks for a quote, price estimate or calculation‘ works. ‘Helps with documents“ does not work, because Claude can't do anything with that.

Short is better. Anthropic’s own guideline is: keep it under 500 lines. If it gets any longer, split it into separate files that you reference from your main file. Claude will only read them when necessary.

Refer one level down. A file that links to a file, which in turn links to another file, will cause problems. Link to everything you need directly from your main file.

No dates and versions that expire. “From September we will use the new rate” is simply wrong in three months' time. Put the current rate in and update it when it changes.

One word for one thing. If you call it a quote in one paragraph and an estimate in the next, Claude has to guess. Choose one.

Give one way, not five. Listing all the different ways it can be done – this way, that way or another way – makes the outcome unpredictable. Choose the way you want to do it.

What we do with it ourselves

A few from our own portfolio, to give you an idea of the kind of jobs that lend themselves to it:

• Invoicing for a client with custom rules. That client refuses invoices without a purchase order number before the service name. That is exactly the kind of rule you forget once and then get back two weeks later. It's now in a skill, along with what needs to happen if an email cannot be matched.
• Schedule work in our project management system. Including the capacity check: if someone is already above 75 per cent, nothing more is added. This skill comes with a separate Python script, as you don’t want to have to recalculate that every time.
• Writing blogs in our own style. Yes, this one too. It states what our texts must comply with and which AI stylistic quirks need to be removed.
• Setting up an SEO project. The fixed order of keyword research, competitors and reporting, so that every project starts the same way.

What they have in common is that they are not impressive AI applications. They are simply written-down procedures. Exactly the sort of knowledge that is normally stored in someone’s head and disappears when that person goes on holiday.

Skills on your own website or application

So far, we’ve been talking about work contained in documents. Skills only become really interesting when Claude can access the system where your work is stored: your WordPress site, your online shop or your own application.

The skill then describes the working method, and the integration gives Claude hands. You often already have such an integration lying around. WordPress has a REST API, most applications have one too, and otherwise you just put an MCP server or a small script next to it that is simply in the skill's folder.

The sort of jobs that goes with:

• Update 300 product descriptions in an online shop, adhering to the writing style and mandatory fields specified in the skill.
• Building a new location page following the same template as the forty already there, including internal links and meta description.
• Pulling the same report from the application every Monday, with the same columns and the same explanation underneath it.
• Go through a pile of old blog posts to check for broken links and out-of-date prices, and save the corrections as drafts.

There are two things you need to specify within the skill itself. Firstly, what is not allowed: do not publish anything without an intermediate step, do not delete anything, and if in doubt, stop and ask. Secondly, where it is allowed to run. Start on staging or with read-only access, and only move to production once you have seen a few times that the result is correct.

Anyone who does the work can write down the working method. The integration and the surrounding permissions are technical, and that is usually where it gets stuck. We build that part into websites and web applications, along with the skill, so that the team can then continue on their own.

The mistakes everyone makes

• A vague description. By far number one. The skill is fine, but Claude never grabs it because it says ‘helps with texts“. If your skill isn't working, check here first.
• Explain what Claude already knows. Three paragraphs about what a quotation is. A waste of space and it distracts from the rules that actually matter.
• Stuffing everything into one file. A 1,200-line skill containing your complete price list. Split that price list off into a separate file.
• Testing on a fabricated example. Always works. Says nothing. Test on real work.
• Never look back. A skill is not a document that you finish. If you notice Claude doing something structurally different from what you intended, adjust the skill. That is usually just one line.

Where you learn further

Anthropic has its own explanation sorted now and that's free. On Claude Academy feature short courses with videos and a quiz at the end.

• Introduction to agent skills, six lessons of about an hour each. That is the shortest route after this article.
• Introduction to Claude Cowork and Claude Code 101, if you still need to choose where you are going to work.
• Introduction to the Model Context Protocol, for integration with your own systems.

Everything is in English, and you'll earn a badge if you keep that up. For those who prefer to dive straight into the tech, there is also a complete nine-hour course on building with the Claude API.

Where to start

Pick something you’ve already explained three times this month. Do that task once with Claude, ask to turn it into a skill, strip out anything unnecessary and test it on a real-world task. Half an hour, and you’ve got it.

If the work you want to automate is carried out via your website, your online shop or your own application, this will involve integration and become a more complex project. That’s what we do. If you’d like to have a chat first about where most of your time is spent, please book a consultation.