How we check our tools and guides

Every number nTools shows comes from a formula or a rule that someone else defined: a standard, an official table, a platform’s published policy. This page explains how the tools and guides are checked against those sources, how they are kept up to date and what happens when something is wrong.

Calculators: recomputed, not trusted

Each calculator explains its formula in its help text, with a worked example. Before an update is published, automated tests run the calculator’s own code and compare its answers with figures worked out separately from the source:

• known answers published with a standard, such as the HMAC test vectors in RFC 4231 or the contrast of #767676 on white, 4.54:1 under WCAG 2.2;
• edge cases that catch common mistakes: birthdays on 29 February, a month without a 31st, week 53 of an ISO year, sales below the break-even point, a local time that does not exist on the day the clocks change;
• the examples shown on each page, which are run again so that the page and the tool cannot disagree.

More than 100 of these test scripts run before each update, together with checks of every page in all six languages, its links and its structured data.

Guides: primary sources, checked twice

A guide that relies on a standard, a law or a platform’s rules is written from the primary source: RFCs and IANA registries for networks, the W3C for colours and accessibility, the IANA time zone database, 3GPP for SMS, the help pages of YouTube or Google for their own rules, and the tax authorities for tax tables. It names that source, most guides in a list at the end, and every guide shows the date it was last updated.

Every fact and figure is checked twice before it is published: once against its source, and once by recomputing it or running it in the tool it describes. Translations are checked against the English text, and a correction is made in every language at once.

Rules that change, and when we look again

Some answers depend on rules that are changed by someone else. These are the ones the site relies on, and when they are checked:

What the results are, and what they are not

The tools give you the arithmetic and the rules as they are published. They are not legal, tax or financial advice, and they do not know your situation: a tax calculation does not include every deduction you may be entitled to, and a freelance or sponsorship rate is an estimate built on numbers you choose. Check anything important with a professional or with the official source named on the page.

Corrections

If you find a mistake, write to [email protected] or use the contact page. A correction is made in every language the page is published in, the page’s date changes, and the latest ones are listed here:

• 5 November 2026 — Colour contrast guide: WCAG 2.2 became a W3C Recommendation on 5 October 2023; 12 December 2024 is the date of its latest edition, not of the Recommendation.
• 5 November 2026 — Time zones guide: added Cuba’s decision not to turn its clocks back on 1 November 2026 (IANA release 2026f).
• 5 November 2026 — Age calculator: a birth date in the future is now named as such, and on the birthday itself the next birthday reads “Today”. Unix timestamp converter: the UTC time is written in the page’s language.
• October 2026 — A review of every tool’s help text found and fixed errors in the tools themselves: birthdays on 29 February, the pre-filled time of the timestamp converter, YAML keys, link schemes in the UTM builder, the match count of the regex tester, Title Case with accented letters, numeric and random sorting, and invalid or half-hour time zones in the meeting planner.