Privacy policy
Last updated 31 October 2026. This page covers this website and the Ostella add-on.
The short version
- Your Anki collection and your chat history stay on your computer.
- To write a reply, Ostella sends the text of your messages, the text of the cards being discussed, and any handout or capture you attach, through our server to Google's Gemini models or to Lithos (GLM 5.3). That is how the AI works; without it there is no reply. For broad questions, short snippets are also sent to a card-picking model run by or for Liquid AI.
- Our server does not store your chats, cards or handouts. It keeps your account, how much AI you used, and a 30-day log of when each AI call happened and how long it took (no text).
- If you press Feedback, the note and the exchange it is about are sent to us.
- If you write to us through the contact page, we keep your message, your reply email and, if you give one, your name, until you ask us to delete them.
- You may give a name, school email, school and how you heard about us. It is optional and you can ask us to delete it.
- Summary usage numbers (counts only, never text) are sent only if you opt in. They are off by default.
- This website sets no cookies and has no analytics or tracking.
What is sent to AI providers, and when
Every time you use the chat, a handout check or a similar feature, the add-on's local program builds a request and sends it to our server, which forwards it to an AI provider and returns the answer. Most requests go to Google's Gemini API; chat replies can go to Lithos (GLM 5.3) instead, and if Lithos cannot answer the add-on retries on Gemini. The request can contain:
- what you typed in the chat, or dictated (see below);
- the text of cards from your deck that match what is being discussed, together with some review statistics for those cards (for example how well you remember them, and how you did on them in earlier Ostella chats);
- the text of a handout you open for checking, and the passages you search for;
- a screen capture you attach: its text, which is read on your computer, or the picture itself if you choose to send it as an image; or the text of a web page you attach with the browser panel;
- the recent conversation, so replies make sense.
For handouts and card lists, the request may be stored briefly at Google as a "context cache" (up to 30 minutes) so that several parts of one check can reuse it; the add-on deletes it when the work is done.
Google. We use Google's paid Gemini API. Google's published terms for paid API services say that it does not use prompts or responses to improve its products or train its models, and that it logs them for a limited period only to detect and prevent abuse (ai.google.dev/gemini-api/terms). Google's terms govern what Google does; please read them. (If you run Ostella with your own key on Google's free tier, Google's terms allow it to use content to train its models.)
Lithos. Lithos says it does not keep your inputs or outputs after processing, apart from what legal, dispute or billing needs (zero data retention by default). Its terms do not say whether it trains models on inputs, so assume it may; we have not found where it hosts them (lithosai.com/terms-of-use).
Liquid AI, via OpenRouter. To pick relevant cards for a broad question, up to 600 characters of your message and up to 200 characters of each candidate card are sent to a card-picking model run by or for Liquid AI through OpenRouter. Liquid's published terms allow it to use submitted content to develop and improve its models.
Please do not enter patient names, record numbers or other identifiable clinical information, in chats or handouts.
What stays on your computer
- Your Anki collection. Ostella reads cards through the add-on and writes to Anki only changes you approve or ask for (ratings, cards you choose to unsuspend, and screenshots you choose to add to cards).
- Your chats, the handout library and results, ratings you confirmed, and a log of what you said about each card.
- The search index of your deck, built on your computer.
- Voice dictation: speech is turned into text by a model that runs on your computer. The audio is not sent anywhere and is not stored; only the resulting text, once you send it as a message, goes to Google like any other message.
- Screen capture pictures are kept on your computer for one day. Pictures are not saved inside chats.
When you set Ostella up, it downloads software and search models from the internet (for example from GitHub, PyPI and Hugging Face), as any download would reveal your network address to those sites.
What our server keeps
| Data | Why | How long |
|---|---|---|
| Your account: an anonymous ID, a secret token (stored only as a hash), the access code you used, your plan and limits, when it was created or expires | To sign you in and apply limits | While your account exists |
| Usage: for each day, how many AI calls you made and what they cost | To enforce limits, run the service and work out costs | While your account exists |
| Subscription: Stripe customer and subscription IDs, and status (active, cancelled, and so on) | To turn Pro on and off | While your account exists |
| Request log: for each AI call, the time, your random account ID, which model was used, whether it worked, how long it took and the size of the request. No text. | To find out why a reply was slow or failed | 30 days, or until your account is deleted |
| Optional contact details: name, school email, school, how you heard about us | To contact beta students about the beta and for account recovery; visible only to the developer, never sold or shared | Until you ask us to delete them |
| Messages sent through this website's contact page: your message, the email address you give for a reply, and your name if you choose to give one. Nothing else is saved with it (not your network address, and no cookie is set). | To read and answer your message (support, data requests, partnerships); visible only to the developer, never sold or shared. We are alerted that a message arrived, but the alert does not contain its text. | Until you ask us to delete it (use the contact page, or include the email you wrote from) |
| Optional summary usage numbers (only if you opt in): active days, turn counts, credits by model, rating-change rates, error and fallback rates, feedback counts. No card or chat text, no name or contact details, only your random account ID | To see how many students use Ostella and what it costs | The latest summary for each week, for up to 90 days; deleted at once if you turn the option off |
| Feedback you send with the Feedback button: your note and the exchange it is about (your message, the reply, the cards involved) | To fix problems and improve Ostella | Deleted automatically after 90 days, or sooner if you ask |
The server does not store the content of your chats, your cards or your handouts. To limit guessing of access codes it counts recent sign-in attempts per network address in memory; this is not written to our database. Our hosting provider (Fly.io) necessarily handles your connection and may keep ordinary server logs. The contact page uses the same in-memory count (at most 5 messages per network address per hour) to limit spam; the address is not saved with your message.
Visitors to this website
This website sets no cookies and uses no analytics or advertising tools, and our web server does not keep a log of visitors. The only script is on the contact page: it sends the form you fill in to our server (api.ostella.app) and loads nothing from anywhere else. Traffic to this website and to our server passes through Cloudflare, which delivers the pages and protects them from abuse; Cloudflare necessarily sees your network address and the pages you request, and may keep ordinary security logs (cloudflare.com/privacypolicy).
Payments
Payments are handled by Stripe. Stripe collects your payment details and email address and sees your payment history. We never see your card number. Stripe's own privacy policy applies to what it collects (stripe.com/privacy).
Who we share data with
- Google (Gemini), Lithos (GLM 5.3) and Liquid AI via OpenRouter, for the requests described above.
- Stripe, for subscriptions.
- Fly.io, which hosts our server.
- Cloudflare, which delivers this website and our server's traffic.
We do not sell your data or show advertising. This website has no analytics or tracking tools. The add-on sends summary usage numbers only if you opt in, as described above.
Your choices
You can ask us to delete your account data and any feedback we hold: write to us through the contact page. You can delete Ostella's data on your own computer at any time by removing the add-on and its data folder. Ostella is for people 18 and older.
Changes and contact
If this policy changes in a way that matters, we will tell you in the app. Questions: the contact page.