Pick a scope an agent can finish.
The tools that work are tiny on purpose: one job, browser-local, no accounts, no backend, nothing uploaded. Think a text diff, a pattern generator, a calculator. That scope fits in one HTML file, which means the agent can build, test, and fix it in a single loop — and hosting it is free anywhere.
What you need.
- Claude Code — included with a Claude Pro plan ($17 a month billed annually, $20 monthly). It runs in the terminal, the Claude desktop app, or the browser.
- An empty folder and a browser to test in.
- One paragraph of intent — see the brief in step two.
From idea to shipped in six steps.
- Install Claude Code and sign in with your Claude account, then open it in the empty folder.
- Write the brief: what the tool does, who it is for, and the constraints — one index.html, inline CSS and JavaScript, everything computed in the browser, nothing sent to a server.
- Let the agent build the first version, then open the file in your browser and use it like a stranger would.
- Report what is wrong in plain language — the agent fixes files directly, so "the copy button does nothing on Safari" is a complete instruction.
- Check the layout at three widths with the free Responsive Preview tool.
- Ship the file to any free static host, and run the Launch Checklist Prompt first — the launch-check guide shows how.
What it actually costs.
A tiny tool costs a subscription, not a development budget. This entire site — every free tool and page on it — has a public build log putting the total at roughly $565 to $825 in AI usage (see the release notes). One tool is a small slice of that. Claude Pro includes Claude Code at $17 a month billed annually — this Claude referral link gets you started.
When a tiny tool is the wrong build.
Accounts, payments, stored user data, or anything sensitive breaks the browser-local model — those need a real backend and real engineering. And if what you actually need is a landing page rather than a tool, a Carrd template is the shorter path.