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Privacy Policy

Effective date: November 5, 2026

This is an English translation of our Datenschutzerklärung. If the two differ, the German version prevails.

1. Controller

Magnus Ohle
Haaggasse 10
72070 Tübingen
Germany
Email: [email protected]

This policy covers the website checkst.app, the iOS app checkst (flashcards) and the iOS app teckst (lecture recording). Both apps come from the same provider and use the same optional checkst account. See also the Impressum. We have not appointed a data protection officer; we are not required to.

2. Summary

  • Both apps work without an account. Flashcards, study progress, recordings, transcripts and notes then stay on your device only.
  • teckst never uploads audio recordings. Transcription runs on the device.
  • We use no advertising, no third-party advertising or tracking SDKs, no social media plugins and no fingerprinting.
  • Data reaches our server when you use a checkst account: for study groups, leaderboards, shared decks and lectures and (with Pro) for sync. Text goes to OpenAI only if you enter your own OpenAI key yourself.
  • When you delete your account, we delete your data. Exception: content you uploaded to a group that continues to exist (section 9).

3. Website checkst.app

3.1 Server and logs

The website and the apps' API (checkst.app/api) run on a Hetzner server in Germany. For every request the server processes IP address, time, requested URL, HTTP status, referrer and user agent. We keep this in server logs:

  • Access log for audience measurement (section 3.3): rotated daily, deleted after about 2 days.
  • Security log (detecting attacks and abuse): rotated daily, deleted after about 8 days.
  • Standard web server logs: rotated daily, kept for up to 52 days.
  • API application log: error messages; for failed sign-in or password reset attempts also the email address used.

To limit requests (protection against automated sign-in attempts and against enumerating preview links) the server counts requests per IP address. These counters live in memory only and are not stored.

Purpose: operation, security and troubleshooting. Legal basis: Art. 6(1)(f) GDPR (legitimate interest in a secure, working service).

3.2 Cloudflare

checkst.app is reached through Cloudflare (Cloudflare, Inc., USA). Cloudflare forwards every website visit and every app request to our server and processes the connection and request data (including IP address, requested URL, user agent). Cloudflare delivers the pages, blocks attacks, protects email addresses on the website from spam bots (Cloudflare adds a small script for this) and may have browsers send network error reports (NEL) to Cloudflare. Legal basis:Art. 6(1)(f) GDPR. Cloudflare is our processor; for transfers to the USA see section 8. Privacy policy:cloudflare.com/privacypolicy.

3.3 Audience measurement (minilytics)

To understand which pages are visited and where visitors come from, we analyse the access log (IP address, user agent, referrer, requested URL, status) with minilytics, a statistics tool we run ourselves. No script is loaded into your browser, no cookies are set and nothing is stored on your device. A background job on our server reads the log and sends only the page path (without parameters), time, coarse device type, the referring site's domain and regularly rotating pseudonymous identifiers to our statistics database; the IP address itself is not sent. The statistics database runs on a server we rent from OVH (France). The access log is deleted after about 2 days. Legal basis: Art. 6(1)(f) GDPR (legitimate interest in improving the website). You can object under Art. 21 GDPR (an email is enough).

3.4 Signing in on the website

When you sign in on checkst.app (account, password reset), your browser keeps the sign-in token and your account data in local storage until you sign out. This is strictly necessary for the function you asked for (§ 25(2) no. 2 TDDDG). Otherwise the website stores nothing on your device.

4. The checkst app

4.1 Without an account

Flashcards, decks, media, study progress and settings stay in the app on your device. We receive none of it. Data leaves your device only in the cases described in sections 4.2 to 4.11.

4.2 iCloud sync (free)

If you turn on iCloud sync, the app stores your collection in your private iCloud database (CloudKit) at Apple. We have no access to it. You manage this data via your Apple ID; deleting your checkst account does not delete it. Apple's privacy policy applies.

4.3 checkst account

For an account we store email address, username and a hash of your password, and optionally an avatar URL, university and degree programme. The app remembers on your device that you accepted the community rules. Password reset codes become invalid once used or expired. Legal basis: Art. 6(1)(b) GDPR (contract). We cannot create an account without email address and password; all core features of the apps also work without an account.

4.4 Sync via your checkst account (Pro)

With Pro the app syncs your collection via our server: notes and cards (content), note types, deck settings, scheduling data (FSRS) and review history including answer time per card. Transfer is encrypted (TLS); on the server the data is stored linked to your account. Media files (images, audio) are stored in Cloudflare R2 in the EU region, under your user ID. Legal basis: Art. 6(1)(b) GDPR.

4.5 Study groups, leaderboards and Frost

  • Groups: name, members, roles, invite code, and decks and lectures that members upload. Group members see your username, avatar and study stats in the group.
  • Study stats: XP, level, streak, number of reviews, cards learned, time of the last review, unlocked achievements, daily progress including study time, and XP per week.
  • Global leaderboard: username, XP, level and streak are visible to all signed-in users, not only your groups. So choose a username that does not have to be your real name.
  • Frost: sender, recipient, group, week and times of gifted Frost days.

Legal basis: Art. 6(1)(b) GDPR (group and leaderboard features are part of the service you use with the account).

4.6 Shared decks, lectures and preview links

Decks (.apkg) and lecture notes you upload to a group are stored for the group; files are kept in Cloudflare R2 (EU). All members of the group can view and download them. A shared link shows a preview without sign-in: for decks the name, card count and group name, for lectures the title, course name, date and group name. Your username does not appear in this public preview.

4.7 Reporting, blocking and moderation

When you report content or people, we store the report, reason, optional note, your user ID and the time. The provider is notified by email (sent via Brevo, section 4.9) with your username and the reported content. Content reported by three different people is hidden automatically until it is reviewed. We store blocks so that you no longer see the blocked person's content; the blocked person is not told. Suspended accounts are stored with a reason. Legal basis:Art. 6(1)(b) and (f) GDPR (a safe service, protecting other users) and Art. 6(1)(c) GDPR where we must handle notices under the Digital Services Act.

4.8 Pro subscription (Apple in-app purchase)

Apple handles the purchase; we receive no payment data. We store product ID, transaction ID, expiry date and status, query the status from Apple's App Store Server API and receive status notifications from Apple (App Store Server Notifications). Purpose: checking Pro status.Legal basis: Art. 6(1)(b) GDPR.

4.9 Emails

Password reset emails and report notifications to the provider are sent via Brevo (France) as our processor. Brevo processes the recipient address and the content of the email. Legal basis: Art. 6(1)(b) or (f) GDPR. Privacy policy:brevo.com/legal/privacypolicy.

4.10 AI card creation

  • On device: with Apple Intelligence the app creates cards locally (Apple Foundation Models). Nothing is sent to us.
  • With your own OpenAI key: if you enter your own OpenAI API key, the app sends the selected text (including text from a PDF or recognised from a photo) directly from your device to OpenAI or to the compatible provider you entered. We see neither the content nor the key; the key is kept in your device's keychain. Processing at OpenAI is governed by your contract with OpenAI (openai.com/policies/privacy-policy); OpenAI is based in the USA.
  • Neither: you can copy text into another app and paste the result. checkst transmits nothing.

4.11 Deck gallery

The deck gallery loads its list and deck files directly from GitHub (GitHub, Inc., USA). GitHub receives your IP address and the request data. Privacy policy:GitHub Privacy Statement.

5. The teckst app

  • On the device: audio recordings, transcripts, notes, slides, scans and timetable stay on your device. Transcription runs on the device (Apple speech recognition). teckst needs no account; microphone, camera and photos are only used after you allow them and only for the respective feature.
  • Sharing a lecture with a group (optional): teckst signs in with your checkst account. It uploads the notes (text) and, if you choose, the slides as PDF; notes are stored on our server, PDFs in Cloudflare R2 (EU). The audio recording is never uploaded. Sections 4.5 to 4.7 apply to shared lectures.
  • Notes with your own OpenAI key (optional): if you enter your own key, teckst sends the transcript text directly from your device to OpenAI to write notes (as in section 4.10). Without a key, notes are written on the device with Apple Intelligence.
  • Formula recognition: teckst downloads the model from checkst.app on first use. Only the usual connection data is involved (sections 3.1 and 3.2); no personal content is sent. Recognition runs on the device.

6. No advertising, no third-party tracking

We use no advertising networks, no third-party analytics or tracking services (such as Google Analytics), no social media plugins and no fingerprinting. We do not sell data and make no automated decisions within the meaning of Art. 22 GDPR. Automatic hiding after three reports (section 4.7) is provisional; a human decides on deletion or suspension.

7. Recipients and processors

  • Hetzner Online GmbH (Germany): server hosting.
  • Cloudflare, Inc. (USA): delivery and protection of website and API, file storage in R2 (EU region).
  • Brevo (France): sending emails.
  • OVH (France): server for our access statistics (section 3.3).
  • Apple: app distribution, in-app purchase, iCloud (Apple's own responsibility or your contract with Apple).
  • OpenAI: only if you enter your own key (your contract with OpenAI).
  • GitHub: only when loading from the deck gallery.
  • Other users: as described in sections 4.5 and 4.6.

8. Transfers to third countries

Our server and file storage (R2) are in the EU. Cloudflare, Apple, GitHub and OpenAI are or belong to companies based in the USA; data may reach the USA in the process. The basis is the European Commission's adequacy decision on the EU-US Data Privacy Framework (Art. 45 GDPR) for certified companies, otherwise standard contractual clauses (Art. 46(2)(c) GDPR).

9. Retention and account deletion

  • Account data, sync data, study stats and group memberships: until you delete your account.
  • Server logs: as set out in section 3.1 (about 2, 8 or up to 52 days).
  • Subscription data: until the account is deleted.

You can delete your account at any time in the app (checkst: Profile › Settings › Account) or by email to[email protected]. We then delete your account, your sync data and media files, your study stats, Frost gifts, memberships, your publicly shared decks, reports by you and about you, and blocks.

Exception, group content: decks and lectures you uploaded to a group that continues with other members stay there for the other members and are assigned to the group owner or, if you were the owner, to the member who takes over the group. Your name is then no longer linked to that content. Groups in which you were the only member are deleted with all their content. Basis for keeping it: Art. 6(1)(f) GDPR (the group's interest in shared study material) and the licence in section 5 of the Terms of Use. If you want such content removed anyway, write to us.

Deleting your account does not cancel a running subscription; only your Apple ID subscription settings can do that. You delete data in your iCloud and on your device yourself (delete the app, or via iCloud settings).

10. Your rights

Under the GDPR you have the right to

  • access (Art. 15),
  • rectification (Art. 16),
  • erasure (Art. 17),
  • restriction of processing (Art. 18),
  • data portability (Art. 20),
  • object to processing based on Art. 6(1)(f) GDPR (Art. 21).

An email to [email protected] is enough.

11. Right to lodge a complaint

You can complain to a data protection supervisory authority, for example where you live or the authority responsible for us: Der Landesbeauftragte für den Datenschutz und die Informationsfreiheit Baden-Württemberg,baden-wuerttemberg.datenschutz.de/beschwerde.

12. Changes

When the apps or the law change, we update this policy. The version published here applies.

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