Subprocessors
Who else handles data when you use Keiko.
The external services behind sign-in, the database, hosting, payments, email, and the AI features — what each receives, and what we have not verified about them.
Last reviewed: August 15, 2026 · Next scheduled review: September 14, 2026
What this list is
These are the external services the application sends data to, taken from the integrations in the code. For each one we state what it does and what it receives.
What this list is not: a legal role determination, and not a claim that a data processing agreement, a transfer mechanism, a region setting, or a provider security review has been put in place and checked. Those are separate facts we have not published, and we will not imply them by listing a provider here.
Always involved when you use an account
- WorkOS — sign-in and sessions
- Handles authentication and issues the session. The application mirrors the account identifier, email address, and first and last name it returns.
- Supabase — application database
- Stores the account record, profile and study preferences, practice attempts and learning evidence, study plans, mock attempts, notebook entries, saved tutor chats, writing attempts and feedback, subscription state, contact and newsletter records, and rate-limit rows.
- Vercel — hosting
- Runs the application and serves every page and route, so it processes ordinary request data such as connection information.
- Stripe — payments and subscriptions
- Runs hosted checkout and the billing portal and sends signed webhooks about subscription lifecycle. Card details are entered on Stripe's own pages; the application keeps Stripe identifiers and minimal subscription state.
Involved only when a feature is used
- Resend — email delivery
- Delivers contact-form notifications and newsletter or welcome emails when email sending is configured. It receives the address the message goes to and the message itself.
- OpenAI — through the ChatGPT account you connect
- Processes tutor prompts, any context you attach, practice essays you submit for feedback, and the generated responses. This runs under the terms of the ChatGPT account you connect yourself, and only for Pro learners who start a request. Disconnecting ChatGPT stops future requests.
Only after you allow the matching choice
- Vercel Analytics and Speed Insights — site-use and performance measurement
- Loaded only after you allow that choice, and only on an allowlist of public content pages. Event URLs keep this site's pathname with query strings and fragments removed.
- Google Analytics — campaign measurement
- Loaded only after you allow Google Analytics. It receives page views for an allowlist of public pages and, for a completed purchase, a one-way transaction code with the amount, currency, and one internal plan code. Advertising storage, personalisation signals, and Google Signals are disabled in the configuration.
What we have not verified
For every provider above, the contracting entity, the processing regions, onward providers, transfer arrangements, retention and deletion behaviour, and security posture are not published here and have not been independently confirmed by us.
A provider's public documentation or a dashboard setting is not evidence that our specific account, project, or region carries that setting, so we do not repeat their claims as though they were ours. We also do not claim this arrangement satisfies any particular data-protection regime.
Changes and review
This page is reviewed on the schedule above, and again before a provider is enabled or removed, when the data a provider receives changes, or when a provider's role in a feature changes. The date at the top moves when the list changes.
We do not currently run a subscription list for provider-change notices. If you need to be told about a change before it happens, write to support@keiko.study and say so, and we will tell you honestly whether we can meet that.
Something on this page looks wrong, out of date, or does not match what you experience? Tell us and we will recheck it. You can also email support@keiko.study. Please leave passwords, payment details, and other people's personal information out of the message.