Cookies and browser storage
ClusterDrill sets no cookies. Not one — first-party or otherwise. There is no analytics, no advertising, no tracking pixel and no third-party script that could set one. What the site does use is a small amount of browser storage on your own device, listed in full below, and all but one entry is required for something you asked it to do.
1. Why there is a choice at all
Dutch law (Article 11.7a of the Telecommunicatiewet, implementing the ePrivacy Directive) requires your permission before storing or reading information on your device — unless that storage is strictly necessary to deliver a service you asked for, or exists only to carry a communication.
Almost everything below is strictly necessary under that test: you cannot stay signed in without a sign-in token, and a drill cannot remember where you got to without keeping your progress. One entry is not necessary, so we ask about that one and honour the answer. We would rather offer a small real choice than a large fake one.
2. Everything stored on your device
All of it is first-party localStorage on clusterdrill.io. None of it is sent anywhere except where noted, none of it is readable by another site, and you can delete all of it at any time through your browser's site-data settings.
| What | Why | How long | Needs consent |
|---|
firebase:authUser:* |
Keeps you signed in between visits. Set and managed by Firebase Authentication, which is Google acting as our processor. |
Until you sign out |
No — strictly necessary |
cd.emailForSignIn |
Holds the address you typed just long enough to complete an email-link sign-in, then is removed. |
Minutes |
No — strictly necessary |
hpcTrainer.v1 |
Your drill progress: which questions you have seen, right and wrong counts, labs solved, best streak. Signed in, a copy is also saved to your account so it follows you between devices. |
Until you clear it |
No — it is the service |
hpcTrainer.theme |
Whether you chose Light or Dark. Written only when you click one. |
Until you change it |
No — a preference you set yourself |
hpcTrainer.consent |
Your answer to the storage question, so we stop asking. |
Until you change it |
No — it records the choice |
hpcTrainer.who |
The optional one. Your email address, so the public pages can greet you and offer "Go to my dashboard" instead of the sales copy. Purely convenience: it authorises nothing, and the app works identically without it. |
Until you sign out |
Yes |
3. What "Essential only" actually does
It is not a flag we set and ignore. Choosing Essential only means hpcTrainer.who is never written, and any copy already on your device is deleted the moment you choose. The public pages will then show you the same thing they show a stranger, even while you are signed in. Everything else keeps working exactly as before, because everything else is necessary.
4. Changing your mind
Nothing here is one-way.
You can also clear site data for clusterdrill.io in your browser, which removes every entry above, including your progress if it is not also saved to an account.
5. Payment pages
Paying takes you to Stripe, on Stripe's own domain. What Stripe stores on your device there is governed by Stripe's own notice and consent, not by this page — we cannot set or read anything on it. See the Terms for who you are contracting with at that point.
6. Server-side records
Separately from your device, we keep account and purchase records on our servers — what those are, why, and for how long is set out in the Privacy Policy. This page covers only what is stored on your own machine.
7. Changes
If we ever add something that genuinely needs consent — an analytics tool, an embedded video, anything third-party — it goes in the table above and into the banner before it ships, not after. Last updated 2 August 2026.
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