Which system do people ask you about all day?
A connector is a small helper that lets Claude look things up in one system. You describe it and Claude builds it, so your description decides what Claude can see.
Pick one with a list in it: members, stock, orders, bookings. The practice kit uses a gym's member list, so you can follow along without your own data.
Make it a question with a clear right answer. Then name what stays out, such as phone numbers or what you pay suppliers.
What does Claude get to see?
Guess before you build anything. The Check shows you.
Show the answer
Only what the connector sends back. Claude doesn't open the file. It asks the connector a question and reads the reply, and your prompt settled what a reply may hold: here, Ana's name, plan and end date. Her phone number is in the file too, but it never reaches Claude.
Show the answer
Claude says it can't. You never asked for a way to change the file, so the connector doesn't have one.
Describe the connector and let Claude build it
Five steps, about 15 minutes. Tick each one when it's done.
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Put the kit in a folder and open it in the Code tab.
Unzip the kit somewhere you won't move it, such as Documents, because Claude Desktop will start the connector from there every time. Open that folder in the Code tab with the mode set to Manual, as you did in course 2, lesson 4.
The Greenfield Gym kit
Greenfield Gym is a made-up gym with 6 members. The ZIP holds members.csv, with each member's name, phone number, plan and end date, and a short README.txt. Unzipping it gives you a folder called greenfield-gym.
Download the ZIP (under 1 KB) -
Give Claude the build prompt.
Paste it into the Code tab and press Enter. It's written like a brief to a colleague who does the work while you check it.
Build me a connector so Claude Desktop can look up our gym members in members.csv, in this folder. It answers two questions: one member's details by name, and whose membership ends within a number of days from a date I give (the last day counts). Each answer gives only the member's name, plan and end date, and nothing else from the file. It only reads members.csv. It never changes, adds or deletes anything. Use what's already on my computer where you can. Before you install anything, tell me what and why. Test it the way Claude Desktop will use it: ask it about Ana, then for 1 November 2026 and 30 days. Show me exactly what it sends back before you say it's done. Then add it to Claude Desktop's settings file as greenfield-gym, keep everything already in that file, and check it starts from there.
It opens with the job and the data.
"It answers two questions" and "Each answer gives only" say what the connector answers and what an answer may hold. Claude will never see more than these two lines allow. The member list also holds phone numbers, and "nothing else from the file" keeps them out. For your own system, this is where you leave out prices or anything else private.
"It only reads" and "Before you install anything" set the limits, on the connector and on Claude.
"Test it" and "Then add it" ask for proof: a test you can read, then the move into Claude Desktop.
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Approve what Claude asks.
In Manual mode Claude stops before each change and waits for your yes. Expect a request to create files in your folder (the connector, one or two files next to members.csv), then requests to run commands while Claude starts the connector and puts your two test questions to it. If your computer lacks something the connector needs to run, Claude should tell you what it is before it asks to install it.
Last, Claude asks to open and change Claude Desktop's settings file, named claude_desktop_config.json. It sits outside your folder, in Claude Desktop's own folder, so Claude asks even to open it. Saying yes adds greenfield-gym to the connectors Claude Desktop starts.
Read each request before you approve it. You can say no to any of them and ask Claude why it needs it. Before it says it's done, Claude shows you what the connector sent back: one line for Ana Pop, then four members for 1 November 2026 and 30 days.
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Ask Claude to explain what it built.
Send this in the same session and read the answer:
Explain what you built as if I've never seen code. One line per file, and one line for anything you changed outside this folder. Then tell me what it can't do.
The answer should say the connector only reads members.csv and gives back only name, plan and end date. If it doesn't, tell Claude which line of your prompt it missed and ask it to fix that.
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Quit Claude Desktop completely and open it again.
Claude Desktop starts its connectors when it opens. Closing the window isn't enough: quit the app (on a Mac, press Command-Q), then open it again.
In a new chat, click + at the bottom of the message box and choose Connectors. greenfield-gym should be in the list.
If you see this instead
- Claude says it can't find members.csv
- The Code tab is open on a different folder. Open the greenfield-gym folder and paste the prompt again.
- Claude wants to install something you didn't expect
- Before you approve, ask: "Why do you need this, and can you do it with what's already on my computer?" If a window from your Mac offers to install developer tools, ask Claude whether it needs them before you click Install.
- The test leaves out Dan Radu, or lists Eva Mocanu
- Claude counted the days wrong. Paste: "Dan Radu's membership ends on 1 December, the 30th day, so he counts. Eva's ended in September. Fix it and test again."
- greenfield-gym isn't under Connectors after you reopen
- Go back to the same Code tab session and paste: "greenfield-gym doesn't show up in Claude Desktop after a full restart. Find out why and fix it." Then quit and reopen again. On a work computer, your admin may have switched off connectors you add yourself.
Does Claude answer through your connector?
Start a new chat in Chat, not in the Code tab, and send this:
In the Code tab Claude can open members.csv itself, so you couldn't tell whether it used the connector. In Chat it has to go through the connector.
You pass when Claude uses greenfield-gym (allow it if Claude asks) and the answer lists four people: Ana Pop (monthly), Cora Dinu (monthly), Dan Radu (student) and Finn Vlad (monthly).
Ben Ilie and Eva Mocanu must not appear. Ben's membership runs to March 2027, and Eva's ended in September. If the reply doesn't show that Claude used greenfield-gym, check that it's listed (step 5), then say "Use the greenfield-gym connector."
Then try "Change Ana Pop's end date to 5 December." Claude should tell you it can't, because your prompt never asked for a way to change the file.
Last, ask "What's Ana Pop's phone number?" Claude should say it can't give you one. The number is in members.csv, but the connector never sends it back. If Claude does give a number, paste this in the Code tab session: "The connector gave out a phone number. It may return only name, plan and end date. Fix it and test again." Then quit and reopen Claude Desktop.
Two questions from memory
You ask in Chat about a gym member. Where does Claude get the answer?
From the connector. Claude asks it and reads its reply, and never opens members.csv. The reply holds only what your prompt allowed: name, plan and end date, and never the phone number.
Why do you quit and reopen Claude Desktop after Claude adds the connector?
Claude Desktop reads its settings and starts its connectors when it opens. Closing the window isn't enough.
Lesson 2 opens by asking the first one again.
It runs on your computer, so it works in Claude Desktop's Chat and Code tab. Cowork and claude.ai in a browser can't use it. A connector the whole team can reach runs on a server and is added as a custom connector. Connectors like these follow an open standard called MCP.
Course 3 so far
What you've built
- Lesson 1: Gym connector