Sudoku Studio — Privacy Notice
Effective date: 20 October 2026 · Version: 2026-10-20.2.
Website: https://sudokustudio.eu
Who is responsible
Serhii Sukhodolskyi, trading as Sudoku Studio, at Av. del Primat Reig, 37, 3-5, Valencia, Valencia, 46019, Spain, is the controller of personal data used to operate this service. Contact [email protected] about privacy or your data protection rights.
Data we process and why
| Data | Purpose and legal basis |
|---|---|
| Username, salted password hash, account identifier and authentication sessions | Create and operate the account and private workspace; performance of the service contract. Passwords are not stored in plain text. |
| Google account identifier, verified email and account link, for Google sign-in | Authenticate and link your account at your request; performance of the requested authentication service. We do not request Gmail, Drive or contact access. |
| Book settings, titles, author names, generated puzzles, exports, history and trash state | Generate, store and deliver your books; performance of the contract. Avoid adding unnecessary sensitive personal data. |
| Generation allowance, subscription state, billing-period identifiers and Stripe customer, subscription, checkout and event identifiers | Control access, fulfil paid orders and prevent duplicate fulfilment; performance of the contract and legitimate interests in reliable billing. |
| IP address and technical request information processed by hosting providers, error events and security records | Operate and secure the service, investigate failures and prevent abuse; legitimate interests in security and availability. |
| Messages and information you send to support | Respond to support, refund and rights requests; performance of the contract, legal obligations and legitimate interests in resolving complaints, as applicable. |
We do not receive full card numbers or card security codes. Stripe processes payment and billing information on its own hosted checkout and portal. Google and Stripe also process information under their own privacy notices. Data is not used to make decisions producing legal or similarly significant effects through solely automated decision-making. Generation and plan limits are operational controls, not credit or eligibility scoring.
Providers and recipients
Render hosts the application and technical logs. Supabase provides the database and private file storage. Stripe provides payments and subscription management. Google provides authentication for public accounts. Apple iCloud Mail handles messages sent to our support address. Authorised operators may access data when necessary for support, security or legal obligations. We may disclose data when legally required, but do not sell personal data or publish private books.
The application server is hosted in Frankfurt, Germany. Providers may also process support, billing, authentication and technical data internationally; choosing an EU application region does not mean all provider processing stays in the EEA. International transfers are subject to the relevant provider's applicable terms and safeguards, such as adequacy decisions or standard contractual clauses where applicable. Contact [email protected] for information or a copy of the safeguards relevant to your data.
Provider privacy information:
- Render: https://render.com/privacy
- Supabase: https://supabase.com/privacy
- Stripe: https://stripe.com/privacy
- Google: https://policies.google.com/privacy
- Apple: https://www.apple.com/legal/privacy/
Account security and abuse prevention
We use signed browser identifiers and keyed hashes of network information to limit automated sign-ins and repeated registrations. These identifiers are used for security, not advertising or cross-site profiling. Short-lived rate-limit counters expire within 48 hours and are removed during subsequent security checks. The legal basis is our legitimate interest in protecting the service and its free allowance. Shared networks may be subject to an additional check or delay.
When a security challenge is enabled, Cloudflare Turnstile processes browser and technical information to distinguish automated requests. Its privacy information is available at https://www.cloudflare.com/privacypolicy/. New-account creation requires server validation of the challenge; a challenge is not proof that different Google accounts belong to different people.
Cookies and browser storage
| Item | Purpose | Duration |
|---|---|---|
sudoku_session | Signed authentication and CSRF session; essential for secure access | Normally a browser session, with server access limited to eight hours; up to 30 days if you select Stay signed in. Logout invalidates authenticated access |
studio_browser | Signed, pseudonymous security identifier for authentication rate limits; not an authentication credential | Up to two days |
studio_language | Remember your selected interface language | Up to one year, or until removed in your browser |
studio_ads_blocked | Remember an explicit refusal of optional advertising; does not affect authentication | Up to 180 days, or until you change the choice or remove the cookie |
studio_analytics_consent | Remember your explicit optional analytics choice; does not identify a visitor | Up to 180 days |
studio_analytics_visitor | Optional signed random browser identifier, only after consent | Up to 90 days |
studio_analytics_visit | Optional visit identifier, only after consent | 30 minutes of inactivity |
| Google sign-in state cookie | Bind a requested sign-in to the initiating browser | Up to ten minutes |
Cookies needed for authentication, request security and abuse prevention operate when needed to provide the service. The language preference follows your explicit language selection. Blocking these cookies in your browser may affect sign-in, security or saved preferences.
During the free beta we do not load AdSense advertising, Google advertising consent scripts, sponsor placements or marketing trackers. No advertising revenue is generated by our integration. AdSense verification metadata and ads.txt do not themselves request ads. Advertising remains disabled independently of your optional analytics choice.
Optional first-party traffic analytics
With your consent, our own server records page views for a fixed list of public and workspace pages, visit timestamps and keyed hashes of random browser/visit identifiers. We use this to understand visits, popular pages and product growth. We do not store raw IP addresses, full URLs, query strings, referrers, browser fingerprints, book contents or third-party tracking IDs in these analytics. If you sign in while consenting, the browser record can be linked to your internal account ID to measure authenticated visitors and attributable signup conversion. These records are pseudonymous personal data, not anonymous data.
Choose Allow analytics or Decline analytics in the optional banner. Declining has no effect on sign-in, books or free allowance. You can reopen Analytics preferences in the footer or workspace at any time, or visit https://sudokustudio.eu/?analytics=settings. Declining after allowing stops collection, removes the current browser identifiers and deletes the traffic records linked to that browser in active storage. Other browsers or previously cleared identifiers require a support request where identifiable. We respect Global Privacy Control and Do Not Track signals by disabling collection.
Page views and inactive browser/visit records are kept for at most 90 days, with expired records removed during subsequent application requests, normally checked hourly. The consent preference itself is kept for up to 180 days. Provider backups expire according to provider lifecycles. Statistics cover only consenting browsers: a browser identifier is not a guaranteed unique person.
Account activity and service operations
Independently of optional traffic analytics, we retain the most recent successful authentication activity and daily account activity for up to 90 days for account operations, service monitoring and security, relying on our legitimate interests in a reliable and secure service. We do not record mouse movements or keystrokes. Requests to erasure or objections can be sent to support. Existing account, generation allowance and book records support account and usage statistics without additional tracking cookies.
Generation outcome, puzzle settings and timing observations linked to internal account/book IDs are kept for up to 366 days to investigate reliability and performance; exception class names (without error messages, URLs or stack traces) are kept for up to 30 days. Daily PDF-response totals contain no account or book identifiers and are kept for up to 366 days. Expired observations are removed on subsequent application requests, checked hourly. Historical billing and book records remain subject to their separate retention purposes below. Only the authenticated owner can access the administrator dashboard. It does not expose passwords, session tokens, OAuth credentials, private files or raw technical logs.
Google may use its own cookies when you open its sign-in service. Cloudflare Turnstile is used for account security as described above. The beta interface is English; older language preference cookies may remain until expiry.
Optional product feedback
After completing a book you may answer an optional survey about satisfaction, ease of use, willingness to pay, a hypothetical preferred price and requested features, and submit two plain-text comments of up to 2,000 characters each. One response is linked to your account identifier, with creation and update timestamps, so you can update or delete it. Please avoid sensitive information. The purpose and legal basis are our legitimate interest in improving the product and researching demand. Participation does not affect your generation allowance, create a purchase obligation or subscribe you to marketing.
Only the owner can access survey analytics, comments and CSV exports. Responses are not published or shared with other users. We do not send survey notification emails. You can delete your response in Feedback or request erasure through support. Account erasure removes its feedback. We retain responses for up to 12 months after their latest update; expired responses are removed on subsequent feedback access, and provider backups expire under the provider lifecycle.
Retention
Account and book data is kept while needed to operate your account and library. Ending a paid subscription does not delete the account or its book downloads. Trash is recoverable archiving, not erasure. Account erasure and data export requests are handled manually after proportionate identity verification.
We erase or anonymise information when it is no longer needed, unless it must be retained for legal obligations, billing records, disputes or security. The applicable retention depends on the purpose, account lifecycle, legal retention requirements and any active dispute. Technical logs and provider backups follow the relevant provider's retention and deletion lifecycle; erasure from active storage does not imply immediate removal from every backup. We do not promise an automatic purge deadline that the service does not implement.
Puzzle fingerprints and technical identifiers support duplicate detection and abuse prevention. Where these can still be linked to an individual, they remain subject to applicable data protection obligations and erasure exceptions.
Your rights and choices
Depending on applicable law, you can request access, correction, erasure, restriction, portability or object to processing based on legitimate interests. Where consent is relied on, you can withdraw it without affecting prior lawful processing. Contact [email protected]; include your username and describe the request. Do not send passwords, card numbers or identity documents unless a proportionate secure verification method has first been agreed.
We respond within the applicable legal period, normally one month for GDPR requests. Any permitted extension will be explained. You may complain to your local data protection authority; for Spain this is the Agencia Española de Protección de Datos (AEPD). Visit the official AEPD website for information and complaints. You do not have to contact us first to exercise that right.
Account services are intended for adults. If you believe a child has supplied personal data, contact us. Material privacy changes will be communicated through the service or another appropriate channel, with an updated effective date.