Privacy Policy

Last updated: 21 July 2026

ChessPrep is a chess opening-preparation app run by an independent developer, Arkadii Kliashtornyi (Germany) — the “data controller”. This policy explains what personal data the app handles, why, and the rights you have. Questions? Email ark.motion.4k@gmail.com.

What we collect

• Account: your username, email address, and password. Your password is never stored in readable form — only a one-way cryptographic hash (PBKDF2) is kept, and it is never sent back to any browser. Your recovery key is stored the same way.
• Your content: the openings and repertoires you create or import, training progress, analysed games, comments, and app settings — so they sync across your devices.
• Social features (optional): if you add friends, your friends list and the chat messages you send are stored so they reach the other person.
• Newsletter (optional): only if you tick the box, we record that you opted in, to email you occasional updates. You can opt out any time.
• On your device: the app uses your browser’s local storage to work and to keep you signed in. We do not use advertising or tracking cookies, and we run no third-party analytics.

Why we use it (legal basis)

• To provide the app and sync your data across devices, and to let you sign in and recover your account — this is necessary to perform our agreement with you (Art. 6(1)(b) GDPR).
• To send the newsletter — only with your consent (Art. 6(1)(a) GDPR), which you can withdraw at any time.
• To keep the service secure and prevent abuse — our legitimate interest (Art. 6(1)(f) GDPR).

Where it’s stored & how it’s protected

Your account and synced data are stored using Cloudflare (Workers KV) and the site is served by Netlify. All traffic is encrypted in transit (HTTPS). Passwords are hashed, each account is protected by its own private access token, and one account can never read another’s data.

Who else is involved

• Cloudflare and Netlify host and store the app and its data on our behalf.
• Lichess: when you open the opening explorer, only the current board position (a chess FEN string — no personal data) may be sent to look up statistics.
• Anthropic (Claude): only if you use the in-app AI assistant, the messages you send it are processed to generate a reply. Don’t put sensitive personal data in those messages.

We do not sell your personal data, and we never share it for advertising.

Your rights

You can access, correct, export, or delete your data. In the app: Settings → Account lets you export a full copy of your data and permanently delete your account (which erases it from our servers). You may also email ark.motion.4k@gmail.com to exercise any of these rights, or to complain to your local data-protection authority.

How long we keep it

We keep your data for as long as your account exists. When you delete your account, it is removed.

Children

ChessPrep is not directed at children under 16, and we don’t knowingly collect their data.

International transfers

Our providers (Cloudflare, Netlify) may process data on servers outside your country, under appropriate legal safeguards such as the EU Standard Contractual Clauses.

Changes

If this policy changes, we’ll update the date above and, for significant changes, notify you in the app.

Contact: ark.motion.4k@gmail.com