Common Tools
Eighteen free tools for money, health, privacy and everyday questions. They run on your device, work offline and show their working.
Money
Borrowing, saving, splitting and spending, worked out to the cent.
Borrow $300,000 at 6.5% a year
- Total interest
- $382,636.71
- Total repaid
- $682,636.71
Health & safety
Act fast in an emergency, and know your numbers the rest of the time.
Compressions a minutePush hard and fast in the centre of the chest, 5 to 6 cm deep, and let it rise fully each time.
Everyday
Units, dates, time zones and QR codes: the small sums of an ordinary day.
Privacy & security
Strong passwords and clean photos, made on your device and never sent anywhere.
Work & study
Check the colours, the words and the grades before anyone else does.
Checked against the source
Each tool shows its formula and links the standard behind it where one exists. Automated tests check the maths against reference values.
- European Resuscitation CouncilCPR rate and depth, 2025 guidelines
- World Health OrganizationBMI categories
- Consumer Financial Protection BureauMortgage insurance, APR and paying down debt
- W3C WCAG 2.2Contrast ratios for text and controls
- ACOGEstimating the due date
- IANA Time Zone DatabaseDaylight saving in every zone
- ISO/IEC 18004The QR code standard
- NIST SP 800-63BPassword guidance
- US Department of EnergyAppliance energy use
- CIPA Exif 3.0What a photo's metadata holds
Private by design
Common Tools runs entirely in your browser. There is no sign-up and no tracking code, so nothing you type ever leaves your device. Every tool shows its formula and, where a published standard exists, links to it, from the Department of Energy's appliance guide to the 2025 resuscitation guidelines. Automated tests check the maths against reference values. Install it once and all eighteen tools open without a connection, on a plane or in a basement with no signal. It is free to use and free to share, with nothing to sign up for. Add it to your phone.
Take it with you
Install Common Tools and every tool opens from your home screen, with or without a signal.
Add to your home screen
- Open this page in Safari.
- Tap the Share button.
- Choose Add to Home Screen, then Add.
- Open this page in Chrome.
- Tap the three-dot menu.
- Choose Install app or Add to Home screen.
On a computer, Chrome and Edge show an install button in the address bar.