Step 1 — The specification comes first
Before a page exists, the calculation is written down: the formula, the input units and their default values, the rounding convention, and the reference the numbers are taken from. For unit conversions that reference is the SI brochure and NIST's conversion tables; for health calculators it is published guidance such as ACOG for pregnancy dating and the AHA/ACSM intensity bands for heart rate; for money it is the standard compound-interest and amortisation formulas; for the kitchen it is the weight-per-cup tables used by professional bakers and the fixed ratios for fresh, active-dry and instant yeast.
Step 2 — One implementation, in plain JavaScript
The tool itself is ordinary front-end code. No framework, no server round trip, no third-party calculation service. That choice is what makes the privacy promise possible: if the maths ran on a server, your input would have to go there too. It also makes the result reproducible — open the page with the network disconnected and the same input still produces the same output.
Step 3 — Verified twice before publication
First against reference values: worked examples with published answers, checked by hand and recorded in the page's explanatory text where a formula deserves showing. Second against an automated regression suite that drives every tool through known inputs and compares the computed output, so a future edit cannot silently break a formula that used to be right. Pages also get checked for the boring failure modes: a unit label that disagrees with the calculation, a default that switches to inches on a metric page, a result that overflows on a small phone screen.
Step 4 — Limits are stated, not hidden
Several questions people ask have no single correct numerical answer, and pretending otherwise is how calculators mislead. Calories per step depend on gait and body mass; bake time depends on pan material, batter depth and oven calibration; fermentation depends on room temperature. In those cases the page says so, shows the assumption it used, and lets you replace the assumption with your own measurement wherever the maths allows it.
What we will not publish
Pages without a working tool. Placeholder pages waiting for content. Clusters of near-identical pages that exist only to catch a long tail of search terms while adding nothing to the answer. And explanation text that is padded for length instead of explaining the method — the article under a tool should tell you how the number was produced, what it assumes and when you should not trust it.
Corrections
If a number is wrong, the priority is to fix it rather than to defend it. Incorrect results reported through the contact page are corrected first, the explanatory text is updated to match, and the case is added to the automated checks. Questions about the method behind any specific page are welcome too; the about page explains who maintains the site, and the privacy policy documents exactly what runs locally and what does not.
Frequently asked questions
How do you check that a calculator is correct?
Each tool is written from a specification that names the formula, units and reference values, then checked twice: against published reference values (NIST and ISO units, ACOG and AHA guidance for health tools, official interest and tax formulas for finance tools) and against an automated regression test that feeds known inputs and compares the output.
Why do some results say “estimate”?
Some quantities cannot be exact: calories burned per step depend on gait and metabolism, bake time depends on your oven and pan material, and fermentation speed depends on room temperature. Where a range is the honest answer, the interface labels it as an estimate and, wherever possible, lets you override the assumed value with your own measurement.
Do you publish pages without a working tool?
No. A page is published only after its tool works and its numbers have been checked. We do not publish placeholder pages, and we do not create clusters of near-identical pages that add nothing beyond a reformatted answer.
What happens when a calculation is wrong?
Report it through the contact page. Reports of incorrect numbers take priority over feature requests: the formula or the reference value is corrected, the explanation on the page is updated, and the fix is kept in the automated checks so the same mistake cannot return silently.