Who we are and how we work
Who we are
Jerusalen Tools is an independent project run by a small team of software developers and technical writers. We build free online calculators that load fast and require no sign-up: tools that answer concrete questions — from a simple percentage to a loan payment — in seconds, without asking for anything in return.
Our guiding principle is straightforward: a good calculator should load instantly, explain which formula it uses, and work just as well on a phone as on a desktop.
Why this site exists
Answers to most everyday calculations already exist online, but they tend to be buried in slow, cluttered pages with confusing explanations. We created Jerusalen Tools to offer the opposite: lightweight tools, instant results, and clear explanations of how each number is produced.
How we build each calculator
Every tool we publish goes through the same process:
- Standard, cited formulas. We do not invent formulas. We rely on recognised references — the WHO criteria for BMI, the Mifflin-St Jeor equation for energy expenditure, standard financial mathematics for interest and amortisation — and we cite them on each calculator's own page.
- Typed code. Every formula is implemented in statically typed code, which reduces errors in units, rounding, and conversions.
- Automated test suites. Before release, every calculation is verified against batteries of automated tests that include edge cases: extreme values, empty inputs, decimals, and negative numbers.
- Ongoing review. If a reference formula changes or we spot an inaccuracy, we update the tool and its documentation.
What we don't do
- We don't give professional advice. Our tools provide indicative results for informational purposes; they are no substitute for a doctor, financial adviser, lawyer, or other qualified professional.
- We don't sell your data. Calculations run entirely in your browser: the values you enter are never sent to our servers.
- We don't claim to be infallible. We work hard to make every result correct, but no software is free of bugs — which is why we explain below how to report them.
How to report an error
Spotted a wrong result, a typo, or a technical issue? Write to us through the form on this site's contact page, mentioning the calculator concerned and the values you used. We review every report and commit to verifying and fixing any confirmed error as quickly as possible, noting the update on the tool itself.