How We Build & Verify Our Tools
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Trust matters most for tools that give you a number. This page explains how every tool on the site is built, checked and maintained.
1. Formulas first
Before any interface is built, we write down the formula and its assumptions in plain language. That explanation is published on the tool page, so you can see exactly how a result is produced and check it by hand.
2. Tested against known results
The calculation logic of each tool is kept separate from its interface and covered by automated tests. For every calculator we collect reference cases — textbook examples, published tables and results from established calculators — and the build fails if our results don’t match. Edge cases such as zero values, negative numbers and rounding are tested explicitly.
3. Runs on your device
Tools run in your browser using JavaScript and WebAssembly. Heavy work such as image or PDF processing happens in a background thread so the page stays responsive. Your inputs and files are never sent to a server.
4. Rounding and precision
Computers store decimal numbers approximately, which can create tiny errors (0.1 + 0.2 = 0.30000000000000004). Our tools clean up these floating-point artifacts and display results to a sensible number of decimal places. Where precision matters — such as loan schedules — the page states how rounding is handled.
5. Keeping data current
Tools that depend on data that changes, such as tax brackets, holidays or exchange rates, list their data source and the date or year it applies to. Yearly data is reviewed at the start of each year, and each page shows the date it was last reviewed.
6. Corrections
If you believe a result is wrong, please contact us with the values you used. We investigate every report, add the case to our tests once it is confirmed, and update the page’s review date after a fix.