Multi-tenant SaaS with Billing

A multi-tenant SaaS platform where organizations can switch between workspaces, data is isolated per tenant at the database level, and billing enforces usage limits automatically across three subscription tiers.

Multi-tenant systems fail in two classic ways: data leaking across tenant boundaries, and billing state drifting out of sync with what a customer actually has access to (especially around failed payments and plan changes).

Clerk handles organization switching and identity, while row-level data isolation in PostgreSQL guarantees one tenant can never read another's data — enforced at the database layer, not just in application code. Stripe subscription webhooks (created, updated, cancelled, past-due) are processed with idempotency keys, and a failed payment automatically triggers plan downgrade enforcement at the API layer.

• →Row-level security in PostgreSQL for per-tenant data isolation, not just query-level filtering
• →Clerk organization switching for multi-workspace identity management
• →Three billing tiers with usage-based limits enforced at the API layer, not just checked in the UI
• →Idempotent Stripe webhook handlers covering the full subscription lifecycle

Keeping billing state consistent with actual access required treating 'payment failed' as a first-class state machine transition, not an afterthought — a downgrade has to be enforced immediately and automatically, not caught later by a support ticket.

Enforcing usage limits at the API layer (rather than trusting the frontend) adds a check to every relevant request, but it's the only way to guarantee a downgraded tenant can't keep exceeding their plan through direct API calls.

Billing state inconsistencies reduced to zero through idempotent webhook handling and automated downgrade enforcement on payment failure.

Add self-serve plan comparison and proration preview before a tenant confirms an upgrade or downgrade.