About ReadoutKit

ReadoutKit is a small collection of single-purpose utilities: loan and savings calculators, unit and currency converters, and image and PDF tools. Each one is built to answer one question and then get out of the way.

Why these tools work differently

Most online converters and compressors work by uploading your file to a server, processing it there, and handing back a download link. That is convenient for whoever built the site, but it means a copy of your document sat on someone else's machine, subject to their retention policy and their security.

Every tool here runs in your browser instead. Modern browsers can resize images, rewrite PDFs, and run any calculation locally at speeds that make server round-trips pointless. Your files never leave your device, which is both faster and a straightforwardly better arrangement for you.

Who runs this

ReadoutKit is built and maintained by Takashi Yamazaki, working alone. The same person writes the code, writes the explanations, and checks the numbers. Nothing here is published as an unreviewed draft by someone else.

Every tool page names its author and the date it was last revised. Tools that depend on figures set by law — tax rates, thresholds, contribution ceilings — list the primary documents they are based on under “Sources” at the foot of the page, together with the date those figures were last checked against them. Income tax calculations follow the published tables of the relevant revenue authority (the IRS in the United States, HMRC in the United Kingdom, the National Tax Agency in Japan) rather than a secondary summary.

The arithmetic itself is covered by automated tests. Each tool's calculation is a pure function, kept separate from its interface so that known values can be pinned down in tests. Mistakes are still possible; if a result looks wrong, please get in touch. Corrections take priority over everything else.

How the site is run

ReadoutKit is an independent project, funded by advertising. Ads are placed below the tool rather than around or on top of it, and we do not use auto-inserted ad formats that appear over the controls. Every calculation shown is free and complete — nothing is held back behind a paywall or a sign-up.

The tools are added gradually, and each one ships with a written explanation of the formula or method behind it. If a result depends on assumptions, those assumptions are stated on the page rather than buried.

Accuracy and limits

The calculators implement standard, publicly documented formulas, and the arithmetic is covered by automated tests. That makes them reliable as arithmetic. It does not make them advice: they know nothing about your circumstances, your jurisdiction, or the specific terms you have been offered. Financial and health tools in particular should be treated as a starting point for a conversation with someone qualified, not a substitute for one.

If you find a result that looks wrong, please tell us. Corrections are the fastest way this site gets better, and we would rather hear about an error than leave it standing.