What the app knows about you.

Who holds it

Kerfox Ltd, a private limited company registered in England and Wales under number 17429118, is the controller of everything described on this page. That means Kerfox Ltd is the company that decides what happens to it and the company you go to about it.

Write to eivan.kolchin@gmail.com about anything on this page. Our complaints page explains what happens if you are unhappy with the answer.

There is a record of you before there is an account

This is the part most apps do not tell you, so it goes near the top rather than buried.

The first time the app opens, it signs itself in as an anonymous user on our backend. You do not do anything and you are not asked. That gives your device an identifier, and it is what lets your progress reach our server at all before you have made an account.

That identifier is not your name, your email or anything you told us. It is a random string. But it is stable, so everything described below is tied together under it: your progress, the record of how you use the app, and anything you report to us.

If you later make an account, that same identifier is kept and your account is attached to it, so nothing is lost. If you sign out, the app returns to a fresh anonymous session and keeps working, which means a record continues after you leave rather than stopping.

You can ask us to delete all of it at any time, with or without an account. How to do that is further down.

What stays on your device

Kerfox is built to work offline, so your device is the first home for nearly everything:

• Your progress: which topics you have studied, what you answered, your streaks and your XP.
• What the memory engine thinks you know, topic by topic, and when it expects you to forget it.
• Your settings, including your study level, your subjects, and whether you use our keyboard or your phone's.
• A queue of usage records waiting to be sent, which holds at most a thousand and then drops the oldest first.

Deleting the app deletes all of that from your device. It does not delete the copy on our server, which is a separate request described below.

What we hold on our server

Our backend is hosted by Supabase. These are the actual tables, named so you can ask us about a specific one:

• Your profile: the study level you picked and the subjects you chose.
• Your progress, but only if you have made an account. This is worth being exact about, because it is the opposite of what most apps do: without an account your progress is never sent to us at all, and the backup exists so that a lost or replaced phone does not lose your work. Make an account and the copy starts; do not, and there is nothing on our server to lose.
• A record of how you use the app, described in its own section below.
• Anything you report to us as wrong, including a snapshot of the question as you saw it and whatever you typed in the note.
• Daily counts of how many times you have used the AI feature, the contact panel and the report control. These exist only to stop any one person exhausting a shared limit, and they are counts rather than content.
• Any badges and XP you have been awarded.

If you make an account with an email address and a password, or sign in with Google, your email address is held by our backend's authentication system so you can get back in. We do not see or store your password, and if you use Google we never receive one.

The record of how you use it

The app sends us a stream of small records about what happens while you study. This is the part worth reading slowly, because it is more than most study apps keep and we would rather you knew than found out.

There are 33 kinds of record. Among them: every answer you give and whether it was right, when a lesson is finished, when a study session ends, when a prediction is made before a reveal, when the app changes how hard it is pitching things to you, when a question is flagged, and, in intensive mode, when a plan is armed, paused, replanned, exited, or when the app judges that you are showing fatigue.

Each record carries a time. Taken together they say when you study, how long for, which days you skip, and where you struggle. We use them to see where the app is failing people, to decide what to fix, and to check whether a change we made actually helped.

Each record also carries which version of an experiment you were in, when we are testing two ways of doing something. That is how we tell whether the new way is better, and it is not a judgement about you.

What permits this is our legitimate interest in knowing whether the thing we built works. You can object to it, and if you do we will stop, and the app will carry on working. There is no penalty and nothing is withheld.

The app decides what to show you next, and that is the point

The memory engine builds a picture of what you know and when you are likely to forget it, and uses it to choose what comes back and when. In data protection language that is profiling, and we would rather say so than pretend a study app that adapts to you does not.

It is on by default and it cannot be turned off, because it is not a feature sitting on top of Kerfox: it is what Kerfox is. An app that showed everyone the same questions in the same order would be a different product rather than a more private version of this one.

It makes no decision with a legal effect or anything close to one. It cannot award you a grade, report you to anyone, or change anything outside the app. It decides which question you see next.

The AI feature, and what leaves the country

The app has an optional feature that turns notes you paste in into practice questions. It is off until you use it, and nothing about it happens unless you do.

When you use it, the text you pasted is sent to Google and processed by their Gemini models. It leaves your device and it leaves the United Kingdom. On the free tier Google may keep it and use it to improve their own models, which is their decision and not ours.

So please do not paste anything into it you would not want kept by a large company you have no relationship with: not your own health information, not anyone else's, not anything private about a person. Notes from a textbook are exactly what it is for.

If we ever move to a different provider, or to terms where the text is not retained, we will say so here and in the app before the change rather than after.

When you tell us something is wrong

The report control sends us the question you were looking at, a snapshot of exactly what was on screen, and whatever you typed. That snapshot is the whole point: it is what lets us reproduce the problem instead of guessing at it, and it is why a report gets a fix rather than a thank-you.

It is tied to your identifier, so we can tell you what happened to your report and award the badge if you were right. Please keep personal details out of the note itself; we only need to know what the app got wrong.

Who else is involved

Three companies, each doing one job:

• Supabase, which hosts our backend: the accounts, the progress copy, the usage records and the reports.
• Google, in two separate ways: the Gemini models, if and only if you use the AI feature, and Google sign-in, if you choose it.
• Cloudflare, which serves the website and the browser version, and therefore sees requests arriving.

That is the whole list. There is no advertising network, no analytics company, no data broker and no third-party tracking in Kerfox. We do not sell your information, we do not share it for advertising, and we do not pass it to schools, colleges, universities or exam boards. Nothing you do in Kerfox is reported to your teacher.

If the law ever required us to hand something over, we would have to. We would tell you, unless we were forbidden from telling you.

Where it goes in the world

Some of it leaves the UK. Supabase and Google are international providers and their systems are not confined to Britain, so we will not promise that your information stays here.

For our backend we rely on the transfer terms Supabase publishes for its services. For the AI feature the text goes to Google under their terms, which is the reason that section says what it says. Write to us if you want to know exactly what covers your information on its way abroad and we will tell you plainly what we have and what we do not.

How long we keep it

Your progress and profile are kept while you are using Kerfox, because that is the thing they are for, and deleted when you ask us to delete them.

Usage records are kept while they are still useful for seeing whether the app works, and we are still learning what that period should be. We will name a fixed period here once we know it rather than inventing one now and quietly changing it later.

Reports are kept while the problem is open and for a period after it is fixed, because a report that comes back is the same report.

Ask us to delete everything and we will, and that means the progress copy, the profile, the usage records and the account itself.

Your rights

You can ask us to do any of these, and it costs nothing:

• See it. A copy of everything we hold about you.
• Correct it. Anything wrong, fixed.
• Delete it. All of it, including the anonymous record described at the top.
• Restrict it. Keep it but stop using it while something is sorted out.
• Take it with you. Your progress in a form you could use elsewhere.
• Object. Tell us to stop recording how you use the app, and we will.

Write to eivan.kolchin@gmail.com. There is no form and no fee, and we will answer within one month. If you do not have an account, say roughly when you started using Kerfox and on what kind of device, and we will find the record.

If you are under 18

Most people using Kerfox are, and this section is written for you rather than for a parent reading over your shoulder.

The rights in the list above are yours. You do not need a parent's permission to use them, and you do not need to explain why. Write to us in whatever words you have and we will work out the rest.

Three things worth knowing specifically. The app records when you study and when you stop, so it knows something about your habits, which is why you can tell us to stop recording it. The AI feature sends what you paste to a company outside this country, so do not paste anything about yourself into it. And nothing you do in Kerfox goes to your school, ever.

If something here worries you, or you just want to know what we hold, ask. We would much rather answer a question than have you guess.

If you are under 13

Kerfox is not for you yet, and we are asking you not to use it. Thirteen is the age at which UK law lets you agree to a service like this on your own, and below it we would need a parent's permission in a way we are not set up to handle properly.

We do not ask your date of birth and we would rather not know it. Making children hand over more about themselves in order to protect them is the wrong trade, so we ask here and trust the answer.

If you are a parent and your child under 13 has been using Kerfox, write to us and we will delete everything held about them.

Changes to this notice

Kerfox is changing quickly, so this notice will change too, and the date at the top says when it last did.

If a change actually affects you, we will not make it quietly. Anything that widens what we collect, or sends it somewhere new, gets said in the app before it starts rather than added to this page afterwards.