One address covers everything below. Most replies go out within a few days; a security report gets looked at sooner.
What to write about
A correction or a wrong result
The most useful kind of message. Every tool here runs on standard formulas, but edge cases exist — leap years, week 53, time zones and rounding all have corners. Tell us which tool you used, what you entered, what it gave you and what you expected. That's usually enough to reproduce it straight away.
Date and time questions are the ones most often reported, and most often subtle rather than wrong: the calculators follow ISO 8601, where weeks start on Monday and week 1 is the one containing the first Thursday. If a result disagrees with another site, that convention is the usual reason.
Privacy questions
The tools do their work in your browser. What you type into a calculator is not sent anywhere, and there is no account system, no server-side profile and no analytics product behind these pages. The one third party is Google AdSense, which serves the single ad unit some pages carry and sets its own cookies.
If you want to know what is stored, why a particular cookie exists, or want a preference cleared, write in. The privacy page covers the general position; email covers the specific case.
Security reports
Responsible disclosure is welcome and will not be met with legal threats. Send what you found, how to reproduce it, and how you'd like to be credited if you'd like credit at all. Please give a reasonable window to fix an issue before publishing it.
There is a machine-readable contact at /.well-known/security.txt for anyone running automated tooling.
Copyright and takedown
If you believe something here reproduces your work without permission, say what the material is, where it appears, and what you'd like done about it. Genuine claims get acted on quickly — usually by removing the material first and discussing afterwards.
What this mailbox is not
It isn't professional advice. The calculators are general-purpose, and results shouldn't be relied on for tax, payroll, legal or financial decisions without checking them against a qualified source — see the terms. Questions about how a number was arrived at are fair game; questions about what you should do with it are outside what a small tools site can responsibly answer.
Feature suggestions are read, but the site stays deliberately small. Each tool is meant to do one thing without an account, an install or a paywall, and most requests that would change that get politely declined.
Getting a useful reply
Include the page URL, your browser, and — for anything involving dates — the exact values you entered. Screenshots help. Everything runs client-side, so there are no server logs to check against; a report without reproduction steps often can't be acted on.