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Architecture

Three layers​

  1. Frontend (browser) — the whole UI, all calculations (financial health, FIRE, projections, insights), in-app notifications, end-to-end encryption of the data, and local mode (localStorage). Works without a server.
  2. Managed backend — Supabase — database (households, subscriptions), Auth, Row Level Security and Postgres functions (access logic running in the database).
  3. Custom server code — serverless functions (/api/* routes in Next.js) needed wherever a secret or a trust boundary is involved — above all payments (webhook, checkout) and sending email / web push.

What needs a server​

  • Payment webhook — verifies the signature and writes subscription status with the service-role key (which must never reach the browser).
  • Creating checkout — calls the provider's API with a secret key.
  • Email / web-push notifications — require scheduling and keys.

What a server is NOT needed for​

Storing the plan, signing in, financial calculations, insights, in-app notifications and encryption — handled by the frontend + Supabase. The encryption key is derived on the device and never sent to the server.

PWA​

The manifest + service worker enable installing on a phone and offline use in local mode. They're also the foundation for future web push.