How We Build and Verify Our Tools

1. The math is verified before the interface exists

Every tool starts as a bare computation that is tested against known-correct values from an authoritative source. Only after the numbers match do we build the interface around them. Some concrete examples of what that looks like in practice:

Our UUID v7 generator reproduces the official test vector published in RFC 9562, the IETF specification that defines the format. The OKLCH color conversions are checked against the reference values published by Björn Ottosson, the creator of the OKLab color space. The retirement calculator's projections are compared with the closed-form future-value-of-annuity formula rather than trusting the simulation loop alone. The contrast checker implements the exact WCAG relative-luminance equations and is validated against the specification's reference colors. Date tools are spot-checked against known ISO week numbers and published US federal holiday observance rules. Loan tools cross-check the amortization schedule against the standard fixed-rate payment formula.

2. Every tool shows its work

Each calculator page displays the actual formula or method it uses, defines its inputs, and states its assumptions — including what it deliberately leaves out. The mortgage calculator tells you it doesn't model PMI; the calorie calculator names the Mifflin-St Jeor equation it runs. If you disagree with an assumption, you can see it and account for it, which is more honest than a black box that just prints a number.

3. Sources are cited — and checked

Where a tool relies on external facts — tax rates, health category thresholds, government pay conventions — the page links its sources, and we verify each linked page actually loads and says what we claim before citing it. Pages that depend on slowly changing reference data carry a "content last reviewed" date so you can judge freshness for yourself.

4. Some tools don't get built

The accuracy bar cuts both ways. A US paycheck calculator is one of the most requested tools on the internet — and we don't offer one, because federal and state withholding tables change every year and we won't publish a calculator whose annual maintenance we can't promise. A tool that is silently one year out of date is worse than no tool at all.

5. Privacy claims match the code

"Runs in your browser" is a testable claim, not a slogan. Tools process your input on your device; the site makes only a small, disclosed set of network calls (live currency rates, anonymous demand voting, analytics, and ads infrastructure), all listed in the Privacy Policy. Anyone with browser developer tools open can confirm this — and we consider that a feature.

Found a discrepancy?

If any Tallyloom tool disagrees with an authoritative reference, that's a bug and we want to know. Report it and it goes to the top of the queue. Tallyloom is built and maintained by Lee and operated by TallyLoom Software LLC — read more about the site.