Multi-tenancy and RLS: a simple definition for B2B SaaS

In short

RLS (Row Level Security) is a database mechanism that limits which rows a user can see, at the server level: each SaaS customer sees only their own data, whatever they do. It is the standard way to isolate your customers' data in a multi-tenant application.

• Isolation is structural: enforced by the database, not by application code.
• Every query automatically checks rights; it cannot be bypassed through the API.
• Works with PostgreSQL, notably on Supabase.
• GDPR compliant: each customer stays strictly isolated.

The problem, concretely

In B2B SaaS, several customers share the same database. Without strict isolation, one customer could see another's data by mistake or manipulation. Secure multi-tenancy addresses this: RLS enforces isolation at the database level, a structural guarantee, not a code promise.

How it works

Each table row carries the tenant (customer) identifier. An RLS policy checks that the user belongs to that tenant before returning the row. Read, write, delete: everything goes through this check. Add authentication (who the user is) and data is isolated end to end.

Why it matters to you

If you are building a B2B SaaS, multi-tenant isolation is non-negotiable: it protects your customers and keeps you GDPR compliant. The building blocks (auth, RLS, PostgreSQL database) are already built and in production on beforbuild.com: I adapt them to your project, at a fixed price from 440 € excl. tax, no subscription. Details on Supabase developer.