Privacy Policy

Overview

Cardstock is an offline-first, account-free flashcards app. Your decks, cards, and study history are stored locally on your device in an SQLite database. There is no account, no sign-up, and studying works fully offline. We do not collect, transmit, or have access to your data.

There is exactly one feature that sends anything off your device, and it stays off until you turn it on yourself: optional AI deck generation, which uses your own API key with the provider you choose. It is described below.

Data You Provide

All of the following is stored only on your device:

• Decks, folders, and cards: terms, definitions, extra fields, and notes
• Images you choose for your cards
• Your learning progress: review history and spaced-repetition scheduling
• App preferences, including your chosen AI provider and model
• Your AI API key, if you enter one (see below)

What We Do Not Do

• No account or sign-up of any kind
• No data collection: we receive nothing about you or your usage
• No analytics or crash reporting in the app
• No fingerprinting, and no tracking of you across other apps or sites
• No sharing of your decks, cards, or study history with anyone, including advertisers
• No internet connection required to study

Ads

Cardstock is free and has no account, and ads are how it pays for itself.

• One placement. A single ad on the screen shown at the end of a study session. Never during a session, never on a card, never interrupting an answer. It is labelled as an ad.
• Non-personalised by default, everywhere. Where consent rules apply you will be asked, and you can change your answer at any time under Settings, Ads, Ad privacy choices. Where no consent rules apply, Cardstock still requests non-personalised ads rather than taking the permission.
• An ad request sends an advertising ID, your IP address, and rough device information to Google, who serve the ad. Nothing from inside the app goes with it: the ad cannot see your cards, your decks, or your study history.
• Watching one rewarded video hides ads for 24 hours, as often as you like, from the results screen or from Settings.
• Ads are served by Google AdMob, under Google's partner policy.

Optional AI Features (Bring Your Own Key)

Cardstock can draft cards from a prompt you write. The feature is disabled until you configure it, and it works on a bring-your-own-key basis:

• You choose the provider (Google's Gemini, OpenAI, DeepSeek, or Anthropic's Claude) and enter your own API key. Any usage is billed to your own account by that provider.
• Your key is stored in your device's secure storage (iOS Keychain, Android Keystore). It is never logged, never shown again after saving, and never sent anywhere except to the provider you chose.
• What is sent depends on the feature, and only ever what it needs. Generating a deck sends the prompt you typed and nothing else. Writing a test, checking a typed answer, and working on a deck send the cards involved, because there is no way to do those things without the material. Your review history and scheduling data are never sent by any of them.
• Cardstock has no server in this path and no key of its own. We never see your prompt, your key, or the result. That request is governed by your chosen provider's privacy policy, so it is worth reading theirs.
• You can remove your key at any time, which disables the feature.

Device Permissions

Cardstock asks for permissions only when a feature needs them:

Photo library: only when you choose to add an image to a card. The image is copied into the app's local storage and is never uploaded anywhere.

Internet: used for ads, for the optional AI features, for backup to your own Google Drive if you switch it on, and to open a link in your browser when you tap one. Nothing else in the app uses the network, and studying never needs it.

Read-Aloud (Text to Speech)

Read-aloud passes the text of the card you are viewing to the speech engine installed on your device, such as Google's or Samsung's. Cardstock does not transmit that text itself.

Note that some device speech engines offer higher quality “network” voices that process text on their own servers. Whether that happens is controlled by your device's speech settings, not by Cardstock. If you would rather nothing left your device, choose an offline voice in your system text-to-speech settings.

Sharing and Importing Decks

A .deck file is a plain, documented ZIP archive that you own. When you share or save a deck, the file is created on your device and goes only where you send it. When you import one, it is read locally and nothing is transmitted.

Deliberately, a deck file contains the content only: your learning history is not included, so sharing a deck never shares your personal study record.

Backups

A backup contains everything the app holds: your decks, cards, images, and your learning progress. Your AI key is never included in one.

Backups you save. Cardstock writes a file to your Downloads folder, and keeps recent automatic copies inside the app. These files are not encrypted, so treat one like any other document you would not hand to a stranger.

Google Drive. Off unless you turn it on. The copy goes to a private folder in your Drive that only Cardstock can see, using a permission that grants no access to the rest of your Drive. It is not encrypted, so Google can read it. You can turn it off and delete the copy from inside the app.

Android's own backup. If you have device backup switched on, Android copies the app's data to your Google account as it does for every app. On Android 9 and later, with a screen lock set, that copy is encrypted with a key derived from your lock screen that Google does not hold. Your Cardstock AI key is explicitly excluded.

Data Retention and Deletion

Because all data is on your device, you are in full control:

• Delete individual cards, decks, or folders at any time
• Remove your AI key in Settings → AI deck generation
• Hide ads for 24 hours from any results screen, or Settings → Ads
• Uninstalling the app removes all of its data from your device

We cannot delete your data for you, and we cannot recover it, because we never have it. Export the decks you care about if you want your own backup.

Website

This privacy page is a static page hosted on khaldoun.dev. It does not use tracking cookies.

Children's Privacy

Cardstock does not collect personal information from anyone, including children.

Future Changes

If a future version of Cardstock introduces features that change these practices (for example, optional banner ads, or a paid unlock), this policy will be updated before those features ship, and the changes will be clearly described. The core promise will not change: your decks and your study history stay on your device, and are never sold or shared.

Contact

If you have questions about privacy or data handling, you can contact:

[email protected]