About MasterTool

MasterTool (mastertool.dev) is a growing library of 1062 free online calculators and converters for practical jobs — pricing a product after marketplace fees, ordering the right amount of gravel, and much more.

Every tool is free

There are no paywalls, trials or premium tiers. Every calculator is fully functional for everyone.

Everything runs in your browser

All calculations happen locally on your device in JavaScript. The numbers you type into a tool are never sent to our servers or to anyone else, and we don't need an account to remember you.

No data collected from tool use

We do not collect, store or see tool inputs or results. See the Privacy Policy for details about cookies and the limited information we receive if you email us.

How we build tools

Each tool page shows the exact formula used, a worked example calculated by the tool itself, reference tables and answers to common questions. Figures that change over time — like marketplace fees — live in dated data tables, and each page shows when its data was last updated.

Contact

Found a wrong result or outdated figure? Want a new tool? Email contact@mastertool.dev or use the contact page.