About HakoTools

What this site is

HakoTools is a collection of small web tools that need no account, cost nothing and run entirely inside your browser. It began in Japanese in July 2026 and is still mostly Japanese: a large part of it deals with Japanese income tax, social insurance and pension rules, which are of no use anywhere else. This English section covers the tools that work the same way in any country.

Hako means box in Japanese. The idea is a box with the tools you need already in it. The site lives at hakotools.com.

How it is run

• What you enter stays in your browser. Salary figures, account balances, a photo of an ID document: you can type or drop any of it in, because none of it is sent anywhere
• Every tool is free and needs no account. No email address, no sign-up, no paid tier waiting a few clicks in
• Ads never sit between you and the tool. They appear below the result and at the end of the explanation, never between an input and the button that acts on it
• The workings are written down. Each tool explains which numbers it uses and how it combines them, with sources where the numbers come from a published table

What "runs in your browser" actually means

Plenty of sites write that they do not send your data anywhere. Here it is not a promise about how the site is operated. It is a statement about what the code does:there is no code path that sends your input anywhere.

A tool's work happens in the JavaScript that the page loaded in order to display itself. Values live in memory and are discarded when you close the tab. Files are read with the File API, processed with Canvas or WebAssembly, and handed back to you as a download. To send any of it to a server the code would have to call fetch or similar, and it does not. If you would rather check than take our word for it, open your browser's developer tools, switch to the network tab, and use a tool while watching it.

This says nothing about the page itself contacting third parties for advertising and analytics, which it does. Those are described separately in theprivacy policy.

Who runs it

One person, as a side project. I work on web applications for a living, mostly on the front end, and I designed, built and operate this site on my own.

The reason it exists: I kept running into moments at work where I wanted to resize an image or split a PDF and the obvious answer was to upload a confidential file to a site I had never heard of. If the work can happen in the browser, that trade disappears, and the tool can be given away for nothing.

• X (@hako_tools)
• Zenn (Mnti)
• Portfolio (mentaimonico)

How the numbers are checked

A calculator that returns the wrong figure is worse than no calculator, so the arithmetic is treated as the part that has to be right.

• The calculation layer is covered by automated tests. They run in full before anything is published, and a single failure stops the release
• Calculation lives apart from the interface. Each tool's maths is a set of pure functions with no access to the page, which is what makes it testable rather than merely tested
• Updated dates mean something. The date on a page changes when its content changed, not to make an old page look fresh
• Estimates are labelled as estimates. Where a result depends on circumstances the tool cannot know, the page says so instead of implying a precision it does not have

Mistakes still get through. Two that were found and fixed: a tax rate table that used one set of bracket boundaries for every household size when the published table varies them, and three PDF tools that produced pages at the wrong physical size because pixel values were passed where the library expected points. Both are described in full on theJapanese version of this page, along with a case where the honest fix was to document a discrepancy rather than hide it. If you find another, pleasetell me.

Money

The tools are free and the running costs are covered by advertising. Those costs are a domain name and hosting, which is the scale the site is aiming at. There is no plan to add a paid tier or a membership.

Ads appear below the result and at the end of the explanation. Their space is reserved before they load, so nothing on the page jumps when they arrive. What the ad and analytics scripts collect is set out in theprivacy policy.

Limits

Results are estimates produced from the assumptions each page states. Where money is involved, real figures depend on circumstances the tool has no way of knowing. Before acting on a number from this site in a way that is hard to undo, check it against an authoritative source or ask a professional. The full terms are in theterms of use.

Getting in touch

Bug reports, corrections and requests for new tools are all welcome on thecontact page.