About Japan Toolbox
- Site name
- Japan Toolbox
- URL
- https://en.dakedane.com/
- Operator
- Japan Toolbox (independent operator)
- Contact
- Contact form (Google Forms; the form labels are in Japanese, but messages in English are welcome)
What this site is
Japan Toolbox is a small collection of free calculators for people who deal with Japanese dates, taxes and measurements but did not grow up with them: visitors, international residents, people buying property, filling in Japanese forms, or working with Japanese colleagues. Each tool explains the rule behind the result, so you can check it yourself.
How we work
- Your input stays in your browser: every calculation runs on your device. Birth dates, prices and other values you type are not sent to or stored on our server.
- We show the rule: each page states the formula, the assumptions and the Japanese law or official source it follows.
- We test the logic: calculations are covered by automated tests whose expected values come from official sources (for example, the Cabinet Office list of national holidays). When a rule changes, we update the tool.
- AI-assisted: the tools and explanations are written with the help of AI (Anthropic's Claude) and checked with automated tests and against official information before publishing. If you find a mistake, please tell us through the contact form.
The site may show advertising in the future to cover its costs. See the privacy policy for details.