What is a Claude skill, and how to use one

First, what a Claude skill actually is

A one-off message is you typing a single question and getting one answer, like "write me a birthday message for my mum". You get a reply, and next time you have to explain the whole thing again from scratch.

A Claude skill is a file of instructions you upload once into Claude, then call with a slash command so it runs the same job every time.

A skill is different. It is a written set of instructions, saved once, that makes Claude do a job the same way every time without you re-explaining it. Think of it like a recipe card: the card does not cook, but hand it to any cook and you get the same dish.

A few words you will see a lot, glossed plainly:

A skill is that reusable set of instructions for one job, built to be kept and used again, not typed fresh each time.
A SKILL.md is the file the skill lives in. The ".md" is a plain-text file type, so a SKILL.md is only text you download and upload, nothing technical to install.
A placeholder is a gap in the instructions marked with square brackets, like [paste your list here]. It is a "fill this in" sign. Some skills ask you to fill those after they load; some just need your own prompt next to them.

So a skill is instructions. Your job is to get the file into Claude, then give it your real input.

How to add a skill in Claude

This is the save-it-once way: download the skill file from a guide, upload it into Claude, then call it whenever you need it.

Open Claude in your browser. Go to claude.ai and sign in if it asks.
Download the skill file from the guide. On the Free Skills page, open the grey skill box and use Download .md (not Copy). That saves the SKILL.md to your computer.
Open Customize, then Skills. In Claude, go to Settings, then under Customize click Skills. Click Add, then Upload skill.
Upload the .md file. Drop the file you downloaded, or click to choose it. Claude runs a short security scan (usually 1 to 2 minutes) before the skill is ready.
Run it with your own job. In a new chat, type the skill's slash name (for the Voice File that is /voice-file), then type what you want done next to it, and send.

One honest note: ChatGPT does not have skills. Its nearest equivalent is a "custom GPT", which is a different thing. This guide is Claude only.

A worked example, start to finish

Take the Voice File from the Make AI write in your voice guide. It makes Claude write like you by learning from real samples you give it.

Open the Voice File guide and click Download .md on the grey skill box.
Open claude.ai.
Go to Customize, then Skills, then Add, then Upload skill, and upload that file. Wait for the scan to finish.
Start a new chat. Type /voice-file, then your job, for example: Draft a 2 sentence Instagram caption about trying a new coffee spot.
Send. Claude uses the skill on your request.

If the skill still has placeholders inside it (sample writing, banned words, never-do habits), fill those when Claude asks, or edit the file before you upload so your real samples are already in it. That is the loop: download the file, upload it once, call it with a slash, add your own job.

Paste or upload: which to use

There are two ways to use a skill, and they are for different jobs. Paste the grey box straight into a chat when you just want to run it once and move on. Upload it under Customize, Skills when you want to keep it and reuse it with a slash command, which is the path this page walks through. A Claude Project is a third option, for standing instructions across a set of chats. When in doubt: paste for a one-off, upload for anything you will run again.

Common beginner mistakes, and the fix

Copying the skill text instead of downloading the file. Copy puts a wall of text in your clipboard; Claude Skills wants the file uploaded. Fix: use Download .md, then Upload skill.
Uploading, then forgetting to give Claude a job. The skill is only instructions. Fix: after it is ready, start a chat, type /skill-name plus what you want done.
Expecting it to remember between chats without installing it. In a plain new chat with no skill installed, Claude starts fresh. Fix: upload it once under Customize, then Skills, so it can load when you call it.
Editing the skill instructions before you understand them. Rewording often breaks the part that made it work. Fix: upload the file as downloaded first; only change placeholders or samples once you have seen it run.

Where the line is

The honest bit: a skill is not magic and it does not check itself. It does the job the way the instructions say, on the input you give it. Feed it thin input, get thin output.
Claude can still get a fact wrong while sounding sure. You are always the one who reads the result before you use it.

Do it now

Pick any guide in the Free Skills library, download the .md, upload it under Customize then Skills, then run it once with a slash command and your own request. Ten minutes, one real thing, and you will have used your first skill.

FAQ

How do I add a skill to Claude?

Download the skill's .md file from the guide, then in Claude go to Settings, Customize, Skills, Add, Upload skill, and choose the file. After a short security scan you run it in a new chat with a slash command.

Should I paste a skill or upload it?

Paste it into a chat for a one-off run you will not repeat. Upload it under Customize, Skills to keep it and reuse it with a slash command. Copy is fine for a quick test, but Download and Upload is the version you keep.

Can I use a skill in ChatGPT?

No. Skills are a Claude feature. ChatGPT's nearest equivalent is a custom GPT, which is a different thing you build separately.