Row Level Security (RLS)
Row Level Security (RLS) is a PostgreSQL feature that controls which rows in a database table a user can read, insert, update, or delete — enforced at the database level, not the application layer.
In depth
RLS is the most important security primitive for multi-tenant SaaS applications. Instead of filtering data in your API routes (which can be bypassed by bugs), RLS enforces data isolation at the database level.
How RLS works in Supabase: 1. Enable RLS on a table 2. Write policies that define who can access which rows 3. Supabase automatically filters rows based on the authenticated user's JWT
Example policy: 'Users can only read their own todos' ```sql CREATE POLICY 'user_todos' ON todos FOR SELECT USING (auth.uid() = user_id); ```
Without RLS, a bug in your API could accidentally expose one tenant's data to another. With RLS, even if your API has a bug, the database refuses to return unauthorized rows.
RLS is non-negotiable for any multi-tenant SaaS storing sensitive data.
Real example
A project management SaaS has 1,000 company workspaces. With RLS, a query for 'all projects' by user from Company A automatically returns only Company A's projects — even if the developer forgot to add a WHERE clause in the application code.
Tools & calculators
Related terms
Technical Debt
Technical debt refers to the implied cost of future rework required when shortcuts or suboptimal solutions are chosen during software development for the sake of speed.
SaaS (Software as a Service)
Software as a Service (SaaS) is a software distribution model where applications are hosted in the cloud and provided to customers over the internet on a subscription basis, rather than installed locally.
API (Application Programming Interface)
An API (Application Programming Interface) is a set of rules and protocols that allows different software applications to communicate with each other — like a contract defining how one piece of software can request data or actions from another.
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