Building a SaaS Invoicing Platform from Scratch

Discovery and tenant model

We mapped org structures, seat vs. usage limits, and approval flows. The data model (organizations, members, plans, entitlements) was defined before a single screen was high-fidelity.

// Tenant-scoped request context
type Ctx = { orgId: string; role: Role };

async function forOrg(ctx: Ctx) {
  return db.invoices.where({ orgId: ctx.orgId });
}

Billing engine with Stripe

We aligned product catalog, metered add-ons, and dunning in Stripe, with webhooks for idempotent reconciliation. Every invoice and payment is traceable in-app for support teams.

API-first, performance budget

We set a 300ms p95 target on core reads and used caching and query shaping on hot paths. Public API docs and versioning shipped alongside the app so partners could integrate early.

// Example: paged, indexed listing
const rows = await db.invoice
  .where({ orgId, status })
  .orderBy("issuedAt", "desc")
  .limit(50);

UI and design system

A compact design system in React kept flows consistent: invoice builder, remittance, and org settings. Accessibility and dense tables were first-class, not a polish pass at the end.