12 min · +200 XP
Build it live
From an empty folder to a tool you have used once.
By the end of this lesson
You will have a working first version of your own tool on your computer, and know how to open it again tomorrow.
Now you build the tool you picked. You need an empty folder, a terminal opened in it and one complete request. The whole first version usually takes from a few minutes to half an hour, depending on the tool.
Mac: make a folder and start Claude in it
- 1In Finder, open the Desktop, right-click an empty area and choose New Folder. Name it after your tool, for example budget.
- 2Right-click the new folder and choose Services > New Terminal at Folder. (If you do not see it, drag the folder onto the Terminal icon in the Dock.)
- 3In the terminal, type claude and press Enter.
Windows: make a folder and start Claude in it
- 1On the Desktop, right-click an empty area and choose New > Folder. Name it after your tool, for example budget.
- 2Open the folder, right-click an empty area inside it and choose Open in Terminal.
- 3In the terminal, type claude and press Enter.
Linux: make a folder and start Claude in it
- 1In the file manager, open your home folder, right-click an empty area and choose New Folder. Name it after your tool, for example budget.
- 2Open the folder, right-click an empty area inside it and choose Open in Terminal.
- 3In the terminal, type claude and press Enter.
When Claude Code opens
- 1It asks whether you trust this folder. It is your own new folder, so choose yes.
- 2Look at the line under the prompt. "⏵⏵ auto mode on" means Claude can work without asking about every file, while a second model checks each action. If you see "manual mode on", Claude will ask before edits; answer the questions, or press Shift+Tab to switch to auto mode if it is offered.
“Build me a budget tool in this folder. I add an expense with a name, an amount and a category; it shows this month's total and a simple chart by category. Save everything on this computer. Large text, calm colours. Make it a single file I can open with a double-click. It is done when I can add, edit and delete an expense and the data stays after I close the page. Decide the details yourself, check that it works, then tell me how to open it.”
Use it as is for a budget tool, or take the request from the card of the tool you picked.
Send the request and let Claude work. You will see it create files and sometimes run commands; this can take a few minutes. If it goes in a direction you do not want, press Esc and say what to do instead.
Open the result
Two kinds of result
- 1A file, such as index.html. Double-click it in the folder and it opens in your browser. It works any day, without the terminal and without Claude.
- 2An address such as http://localhost:5173. This is a small server running on your own computer. Open the address in your browser. It answers only while that server is running; when you close the terminal, the page stops opening, but your files and data stay in the folder.
- 3For a first tool, a single file is the simplest choice. You can ask for it in the request, as in the example above.
Build your tool
0/6“Put a shortcut to my tool on the Desktop so I can open it with a double-click, and check that the shortcut works.”
Claude makes the shortcut for your system and tests it.
A file result: double-click it or its desktop shortcut. A localhost result: open a terminal in the project folder, run claude --continue and paste the first phrase below. If you would rather not do that each time, use the second one.
“Start my tool and give me the address to open in the browser.”
Claude starts the local server and gives you the address.
“Make a desktop shortcut that starts my tool's server and opens the page in the browser, or turn the tool into a single file I can double-click if that works just as well. Check it.”
After this you no longer need the terminal to open the tool.
Ask Claude to initialise a Git repository and commit after the first working version, so every later change has a way back. /init writes a CLAUDE.md with how the project is built and run. The bundled /run skill launches and drives the app, and /run-skill-generator records the launch recipe as a project skill so later sessions do not have to rediscover it.
Claude gave you http://localhost:3000, and the next morning the address does not open. What happened?
Facts checked against the official Claude Code docs October 24, 2026 · source
Author
Evgenii Arsentev
PhD · Chief Executive Officer, digital health