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Editorial standards

How we research, test and correct the tools, and where AI fits in.

Last updated 8 October 2026

The short version

  • Numbers come from primary sources, and each tool names them.
  • Worked examples run as automated tests, and every release is checked in five browsers.
  • AI never calculates a result. Code we wrote and tested does.
  • Found a mistake? Tell us and we’ll fix it.

Research

We start from primary sources: published research, official guidelines and standards, and the original data files. When a source has a version or a date, the tool says which one it uses, for example the CDC 2000 growth charts in the kids growth calculator, the IANA time zone database version behind the time zone converter, or the date AI model prices were last checked. We don’t invent statistics, and we don’t put names of experts or reviewers on tools. Each tool shows its method and its sources instead.

Testing

  • Worked examples. Examples with known answers run as automated tests, so a change that breaks one of those answers can’t be released. Every new tool comes with at least one, worked out independently.
  • Five browsers. Before each release, the pages are opened in Chrome, Firefox and Safari on a laptop, and in Chrome and Safari on a phone. A page fails on any error, if it doesn’t fit a phone screen, or if the page in the browser doesn’t match the page we built. For large sets of similar pages, such as the exercise and conversion pages, a sample runs in all five and every page runs in Chrome.
  • Accessibility. An automated accessibility check (axe) runs on every page in light and dark mode. A new page must pass with no serious problems; known problems on older pages are recorded and the list may only get shorter. Every colour theme is checked for readable contrast.

How we use AI

  • AI never does the maths. Every result is worked out by ordinary code. Where a tool offers AI help, such as explaining blood sugar trends or rewriting text in the Markdown editor, the AI only puts things into words. On health and money pages, an answer that mentions a number the tool didn’t give it is thrown away.
  • On your device first. AI features use your browser’s built-in model, so your text stays on your device. If you choose to add your own AI key, your text goes from your browser straight to that provider, never through us (see the Privacy Policy).
  • AI helps us build. We use AI assistants to help write code and explanations. The sources and the tests above decide whether a tool is right.

Corrections

If a result looks wrong, use Report a mistake in the tool’s ⋯ menu, or the contact form. The form fills in which page you were on, but not what you typed; add the details you’re happy to share.

We aim to look at every report within a week. A wrong result is fixed before any new work. Fixes are listed in the tool’s change log, and the page’s “Updated” date moves. If you leave an email address, we’ll tell you what we found.

Privacy by design

The tools run in your browser. What you type isn’t sent to us, and what a tool saves stays on your device, with no account. Google Analytics counts which pages are visited, never what you enter, and you can turn it off. The details are in the Privacy Policy.