About ZTool

ZTool is a collection of free online tools for the small jobs that come up every day. You might need to format a messy JSON file, check how much a loan will really cost, or convert a recipe from cups to grams. We built each tool to do one job well and get out of your way.

How we build tools

Every tool runs on your own device. We don't upload your text, files or numbers, and we don't need an account to remember you. Pages are pre-built as plain HTML, which is why they load in a fraction of a second even on a weak mobile signal.

How we check accuracy

Calculators follow published, standard formulas. Examples include the standard amortization formula for loans and the Mifflin–St Jeor equation for calorie needs. Each guide shows the formula we use so you can check the math yourself. Before a tool goes live we test it against hand-worked examples and edge cases such as zero, negative and very large values. If you spot a mistake, please tell us and we will fix it quickly.

What our results are, and what they aren't

Our financial and health calculators give estimates for planning and learning. They don't replace advice from a qualified professional who knows your situation.