How we build and verify our tools
Four steps stand between a formula and a live calculator on this site — including the one most calculator sites skip, which is proving the worked example against the tool rather than proofreading it. This page is all four, plus where we stand on AI and what we do when we get something wrong.
Every tool starts with a source, not a guess
Before anything is built we find the authoritative formula and record where it came from — HMRC for UK tax and stamp duty, the NHS and WHO for health metrics, published engineering and physics references for the simulators. That source is cited on the tool’s page so you can check it yourself. If we cannot trace a figure to a primary source, we don’t publish the tool.
We verify the arithmetic numerically, not by eye
This is the part most calculator sites skip. Every worked example on this site is computed independently in a script and checked against the live tool. The numbers printed on the page and the numbers the calculator produces are proven to match — not proofread, executed. If they diverge, the page does not ship.
Every tool passes a fixed checklist
No tool goes live until it meets our full standard: verified maths, sensible handling of empty or impossible input, the formula shown in plain English, a worked example, stated assumptions and limitations, and source citations specific to that tool. An automated check runs across the whole site and must report zero errors before anything is deployed.
We tell you what a tool does not do
Every calculator has limits. A mortgage calculator that ignores fees, or a calorie estimate that cannot know your metabolism, is useful only if you know that going in. Each tool states its assumptions and where it stops being reliable.
Our use of AI
We use AI tools to assist with drafting and development, always under human direction. Nothing is published automatically. Every formula, figure and worked example is verified by a person against its source before it goes live, and the responsibility for what appears on this site is ours, not a model’s.
Corrections
If something is wrong, we want to know: admin@toolcorner.net. We fix errors rather than quietly leaving them, and every page shows when it was last updated.