How we build our tools

We want you to know exactly how the tools on this site are made, so you can decide how much to trust them.

AI-assisted, human-reviewed

We use AI models to help write the code, the tests and first drafts of the explanations. Nothing is published straight from a model. Each tool goes through:

• Automated tests for the calculation itself, including edge cases such as empty input, very large input and unusual characters. A tool cannot be published with fewer than ten passing tests.
• Review of the logic and the text by a separate reviewer, checking that the method is correct, that facts have a source, and that the page is not padded.
• Automated checks that block a tool if it tries to send your data over the network, if its text is too similar to another page on the site, or if its title duplicates another tool.

Your data stays on your device

All calculations run in your browser. The site's security policy forbids the tool code from making network requests, so the text or data you enter is never uploaded.

Few tools, each worth using

We add tools slowly and only when we can do something better or more specific than what already exists. Tools that people don't find useful are improved or removed.

Corrections

Every tool shows the date it was last reviewed. If you find a mistake, please use the contact page.