Privacy Policy

Last updated: 21 October 2026

Vitero Corp s.r.o., a company incorporated in the Czech Republic (company reg. no. 10675400), with registered office at Primátorská 296/38, 180 00 Prague 8, Czech Republic ("Whyston", "we", "us"), operates the whyston.com web application and the Whyston PowerPoint add-in, and is the data controller for personal data processed through the Service. This policy describes what data we collect, how we use it, and your rights.

1. Data we collect

We collect the minimum data needed to operate the service:

• Account information — email address and display name, collected when you sign up via email/password, Google OAuth, or Microsoft SSO (add-in only).
• Usage metrics — generation count, token usage, and estimated cost per API call. Used for quota enforcement and service monitoring.
• Projects, decks and workspaces — the projects you create, the decks (slides, outlines and their generation blueprints) you generate and edit in the web app, and the workspaces and share links you set up. These are stored so you can come back to your work.
• Sources you upload — files you add to a project (e.g. PDF, PowerPoint, Word, Excel, images) are stored in private storage. We extract their text, figures and images into a structured "Evidence Wiki" that grounds your decks; the extraction is performed by AI model providers (see section 4).
• Generated images — images created by AI image generation for your slides are stored so your decks can display them. They are served from links containing a long random identifier that is not listed or discoverable, but anyone holding such a link can open the image.
• Generation artifacts — blueprints and slide data produced during each generation run are kept temporarily for debugging and cost attribution (see section 5). In the PowerPoint add-in, the presentation is assembled into a PowerPoint file and returned to your session for insertion; we do not retain that .pptx file after it is delivered.
• Web research — when web research is enabled for a deck or you ask the assistant to search the web, the search queries derived from your request are sent to our AI provider's web search tool.
• Conversation history — messages exchanged with the AI assistant are stored so you can resume conversations. You can delete conversations at any time.
• About your work (optional) — when you first sign in we ask, optionally, about your role, industry, organisation size, company, main use and how you heard of us. We use the answers to improve and position Whyston; your company name is not shared with analytics providers.
• Product update emails (optional) — if you turn on the monthly summary (at sign-up, in Settings → Account or in the app's "What's new" panel), we record your choice, when you made it and where, and email you a short summary of product changes at most once a month. The legal basis is your consent; you can withdraw it at any time with the unsubscribe link in each email or the switch in Settings. We also note which product updates you have already seen in the app.
• Feedback you send — messages sent with "Send feedback", with your email address and the page you were on, so we can follow up and tell you when a reported issue is fixed.
• Preferences — theme, default overlay settings, saved prompts, and image generation defaults.

2. Data we do not collect

• In the PowerPoint add-in, we do not read, store, or transmit the contents of your open PowerPoint document beyond what you explicitly send to the AI assistant or generation prompt.
• We do not use your content to train AI models, and our AI providers process it under API terms that exclude training on it.
• We do not use advertising trackers or advertising cookies.
• We do not sell or share your data with third parties for advertising or marketing purposes.

3. Cookies & local storage

• Session cookie — a secure, httpOnly authentication cookie managed by Supabase. Required for sign-in.
• Interface preferences — theme, dismissed tips and similar settings, stored in your browser's localStorage (non-sensitive).
• Product analytics (optional) — we measure how Whyston is used (pages visited and key actions such as creating or exporting a deck) with PostHog, hosted in the EU. Without your consent this runs without cookies or local storage and without your IP address. Only if you click "Allow" in the banner do we store an identifier so returning visits can be recognised, and record which elements you click and how far you scroll (heatmaps). All text on the page and in your decks is masked before anything is sent, and no session recordings are made. You can change your choice by clearing this site's data in your browser.

All fonts are served from whyston.com itself; your browser does not contact third-party font services.

We do not set advertising cookies. The optional analytics identifier above is the only non-essential storage, and only with your consent.

4. Third-party services

To provide the service, your data may be processed by the following third parties: (the current list with locations is on our Company & subprocessors page)

• LLM providers — your prompts and generation inputs are sent to one or more AI model providers for slide generation and assistant responses. We currently use OpenAI (deck generation, the assistant and web research), Google (Gemini, partly via Google Cloud Vertex AI in the EU) (reading and extracting uploaded sources) and Anthropic; we may add or change providers in the future. These providers are primarily located in the United States. They process your data as our processors under API terms that exclude using it to train their models.
• Supabase — authentication, database, file storage and row-level security, hosted in the EU (Ireland). Subject to Supabase's privacy policy.
• Vercel — hosting, serverless functions (run in the EU, Dublin), and structured log storage. Subject to Vercel's privacy policy.
• PostHog (EU cloud, Frankfurt) — product analytics as described in section 3. Signed-in users are identified by an internal user id, not by email. Subject to PostHog's privacy policy.
• Sentry — error monitoring: when the app crashes, technical details of the error (not your deck content, IP address or cookies) are sent so we can fix it. Subject to Sentry's privacy policy.
• Resend — delivery of transactional emails such as share invitations and service notifications, and of the monthly product update email if you turned it on. Subject to Resend's privacy policy.
• Linear — our issue tracker. Feedback you send from the app, with your email address and the page you were on, is filed there so we can track and fix it. Subject to Linear's privacy policy.
• fal.ai — optional image generation (Ideogram, FLUX models). Only used when you explicitly request image generation; the image prompt is sent to fal.ai and the underlying model providers. Subject to fal.ai's privacy policy.
• Polar — payment processing and subscription management for paid plans. When you subscribe, Polar (acting as our payment processor) handles your billing and payment information. Subject to Polar's terms and privacy policy.
• Microsoft — OAuth token validation for the PowerPoint add-in's SSO flow. No document content is sent to Microsoft through our service.
• Google — used in two distinct ways: (a) as an OAuth sign-in provider, where only authentication tokens are exchanged; and (b) as an LLM provider (Gemini), where prompts and generation inputs may be sent for slide generation (see "LLM providers" above).

5. Data retention

• Generation artifacts (per-run debug snapshots of blueprints, slides and composition specs) — retained for up to 30 days for debugging and cost attribution, then deleted. Aggregate cost and usage totals are retained longer for billing.
• Projects, decks and uploaded sources — retained until you delete them or delete your account. Archived items are kept until your account is deleted.
• Generated images — retained so the decks that use them keep working; images cannot be linked back to an individual account, so they are not removed automatically when an account is deleted. Contact us to have specific images removed.
• Conversation history — retained until you delete it, or until your account is deleted.
• Usage counters — aggregated monthly totals retained for quota enforcement and billing.
• Account data — retained until you delete your account.

6. Your rights

You can download a copy of your data and permanently delete your account yourself at any time from Account settings. Deleting your account erases your account, workspaces, projects, decks, uploaded sources and conversations. You may also exercise the following rights by contacting us:

• Access — request a copy of the personal data we hold about you.
• Deletion — request deletion of your account and all associated data.
• Rectification — request correction of inaccurate personal data.
• Portability — request your data in a machine-readable format.
• Objection & restriction — object to, or request restriction of, processing based on our legitimate interests.
• Withdraw consent — where processing is based on your consent (e.g. optional image generation), withdraw it at any time, without affecting processing already carried out.

We will respond to requests within 30 days. If you are in the EU/EEA, you also have the right to lodge a complaint with a data protection supervisory authority — in the Czech Republic, the Office for Personal Data Protection (Úřad pro ochranu osobních údajů, uoou.gov.cz).

7. Legal basis & international transfers (EU/EEA)

Where the GDPR applies, we process your personal data on the following legal bases:

• Performance of a contract — to provide the Service (account, generation, the AI assistant, and delivery of your presentation).
• Legitimate interests — usage metrics, quota enforcement, security, error monitoring and debugging.
• Consent — optional features such as AI image generation, which run only when you request them, and the analytics identifier stored in your browser.

Your account data, projects and files are stored in the EU. Some of our processors are located outside the EU/EEA, including in the United States — for example the LLM providers (OpenAI, Google, Anthropic), fal.ai, Resend, and Polar, and Vercel's global edge network. Where personal data is transferred internationally, we rely on appropriate safeguards such as the European Commission's Standard Contractual Clauses.

8. Security

All data is transmitted over HTTPS. Database and file access is governed by row-level security policies — each user can only access their own data and the projects explicitly shared with them. Uploaded files are kept in private storage. Generation is performed using Whyston-managed provider accounts, so your prompts and inputs are sent to the LLM providers on your behalf; if you choose to supply your own API key for direct LLM access, it is never stored on our servers.

9. Children

Whyston is not directed at children under 16. We do not knowingly collect personal data from children.

10. Changes to this policy

We may update this policy from time to time. Material changes will be communicated via the email address associated with your account. Continued use of the service after changes constitutes acceptance of the updated policy.

11. Contact

For privacy inquiries or to exercise your rights, contact the data controller, Vitero Corp s.r.o., at privacy@whyston.com.