Short version: no cookies, no identifier, and none of the figures you type into a calculator are ever stored. That is why there is no cookie banner — there is nothing to ask you about.
When you use a tool, it records the shape of what happened so I can tell whether the tool is any good — never the numbers themselves:
| What | Why |
|---|---|
| Which tool, and which version of it | To tell the tools apart |
| Which fields and buttons you used — not the values you entered into them | To see which parts confuse people |
| Whether you reached a result, and whether it hit a problem | To see whether the tool actually answers the question |
| Which vote option you picked, and whether you left an open-box answer | The feedback that decides what gets built next |
| A random id for the visit | Kept in memory only. It is gone when you close the tab, and is never stored on your device |
| Your country and screen width | To know whether pages work on phones, and roughly where people arrive from |
To count how many people used a tool on a given day, the server makes a one-way fingerprint from your IP address, your browser’s user-agent string, a secret, and today’s date, then throws the original away. Only the scrambled result is stored.
Because the date is part of it, the result is different tomorrow. It cannot be used to recognise you on a later visit, and it cannot be turned back into your IP address. Your IP is never written down. This is the same approach used by privacy-focused analytics tools like Plausible and Fathom.
If you sign up, your address goes straight to Brevo, who run the mailing list. It is not stored on this site at all. Brevo sends you a confirmation email and you are only added if you click the link in it — nothing happens before that click.
Every email has a one-click unsubscribe. Because your address only ever lives in Brevo, unsubscribing removes it completely — there is no second copy here to be forgotten about.
UK GDPR gives you the right to see what is held about you, correct it, or have it deleted. For the email list, use the unsubscribe link, or ask me and I will remove you.
For the usage counting, there is nothing to retrieve or delete, and that is deliberate rather than evasive: the records are not connected to any person, including you, so there is no way to find “yours” among them. That is the point of collecting it this way.
If you switch a tool between light and dark, that choice is remembered on your device so the page looks the same next time. It is not a cookie, it is never sent to the server, and it is not used to identify you. It only exists because you clicked it.
On Cloudflare. Brevo, who handle the email list, are based in the EU.
If anything here is unclear or you think it is wrong, the box at the bottom of any tool comes straight to me.