Tools & Calculators is a collection of 57 small, single-purpose calculators and converters. Each one loads fast, works without an account, and tries to explain its own result rather than just printing a number.
Almost everything runs in your browser. The statistics, finance, text, date and developer tools do all their arithmetic locally, which means your inputs are never transmitted to a server and never logged. Two exceptions need outside data: the currency converter fetches exchange rates, and the IP lookup necessarily involves a request that reveals your address.
The statistical and financial functions are unit-tested against published reference values - textbook critical values for the distributions, standard worked examples for the amortisation and compound interest formulas. That does not make them infallible, and none of it is professional advice. The finance tools are planning aids, not recommendations; the health tools are screening indicators, not diagnoses. If a result matters, check it against a second source.
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If a calculation looks wrong, it might be. Reports of errors are genuinely welcome, as are requests for tools that do not exist yet. You can subscribe for updates when new tools are added.