The short version
Keigo Companion is local-first. Your drill and scenario progress lives in this browser's local storage unless you choose to sign in. Signing in is optional and only adds syncing that same data across devices. There are no ads, no analytics scripts, and nothing here is sold or shared with data brokers.
What's stored, and where
In this browser, always: verb-drill and scenario progress, accuracy stats, your light/dark theme choice, and a daily counter for the optional AI-explanation feature. None of this leaves your device unless you sign in.
If you sign in (optional): your email address, used only to send the magic sign-in link via Supabase Auth, and the same progress and stats data, synced to a database row tied to your account so it follows you across devices. Every row is scoped to your account alone.
Third parties involved
- Supabase — handles sign-in and, only for signed-in users, stores the synced progress data.
- Anthropic (Claude Haiku 4.5) — used only for the optional "explain why" fallback on a missed drill question, and only after a free rule-based check can't classify the mistake. What's sent is the verb, the register, your answer, and the correct answer — never your email or account identity.
- Vercel — hosts the app itself, with the standard server logs any web host keeps.
What we don't do
No ads, no ad trackers, no analytics scripts, no third-party sign-in beyond Supabase's own email magic link, and no selling or sharing of your data.
Your controls
Export or clear your local progress anytime from Settings. Signing out stops any further syncing. To have your account and synced data deleted entirely, open an issue on the project's GitHub repository — there's no separate support desk behind this project.