Last updated: 10 October 2026
There are no accounts, no ads and no tracking. Your stacks, cards and study history stay on your device. We collect anonymous usage statistics to see which features get used, Apple and RevenueCat handle subscriptions, and — only if you choose to generate cards from a PDF — that document's contents are sent to our server and on to Anthropic's Claude so the cards can be written.
Your stacks, cards, images, tags, review history and settings are stored locally on your device and shared with the FlashStacks widgets on the same device. They are not uploaded to us, and we cannot see them. There is no account to create and no cloud sync.
Deleting the app deletes this data.
We use TelemetryDeck to understand how the app is used — for example how many people finish onboarding, whether they choose language learning or their own content, how many stacks they have, and whether card generation succeeded or failed.
Each event is sent with basic technical information (app version, iOS version, device model, language and region) and an identifier that is hashed before it leaves your device and rotates over time. TelemetryDeck is based in the EU and processes this data on our behalf.
What is never included: your name or email, your location, the contents of your cards or the names of your stacks, the documents you generate cards from, your Apple ID, the advertising identifier (IDFA), or anything that lets us identify you or follow you across other apps and websites. We do not track you, so the app never asks for tracking permission.
If you use the AI card generator, the app reads the PDF you choose and sends its contents — extracted text, and images of pages that are mostly diagrams — to our server (a Cloudflare Worker), which passes them to Anthropic's Claude API to write the flashcards. The generated cards come back to your device.
Our server does not store your document or the generated cards; it passes them through and keeps nothing. Anthropic processes the content to produce the response and, under their commercial API terms, does not use it to train their models.
This only happens when you pick a file and tap generate. Please don't upload documents you aren't allowed to share with a third party.
The same applies on a smaller scale to quiz mode: when the app builds multiple-choice options, the question and its answer are sent through the same route.
FlashStacks Premium is an optional subscription. Payment is handled entirely by Apple — we never see or store your card details.
We use RevenueCat to check whether a subscription is active across your devices. RevenueCat receives the App Store purchase record, an anonymous customer identifier generated for your installation, and your App Store country. It does not receive your name, email or Apple ID.
Study reminders, the "deck ready" notification and the Dynamic Island / Lock Screen Live Activity are created on your device and shown by iOS. Their contents are not sent to us.
App data lives on your device until you delete a card, a stack, or the app itself.
Anonymous usage events are kept by TelemetryDeck as aggregate statistics. Because they contain no identifier that we can trace back to a person or a device, we cannot locate or delete an individual's events — there is nothing to look them up by. You can stop any further events at any time with the switch in Settings → Privacy.
Document contents sent for card generation are not retained by us at any point.
FlashStacks is not directed at children under 13 and we do not knowingly collect personal information from them.
We aim to comply with the GDPR (EU/UK) and CCPA/CPRA (California). We do not sell or share personal information as those laws define it, and we do not use data for advertising or cross-app tracking. Our legal basis for anonymous usage statistics is legitimate interest in maintaining and improving the app. Where you ask us to generate cards from a document, we process that content to perform the service you requested.
We may update this Privacy Policy from time to time. Any changes will be reflected on this page with an updated date.