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Supabase Row Level Security (RLS) can enforce row-level rules inside PostgreSQL, but enabling it is not a complete authorization design. Your team still has to decide which roles can attempt each operation, write policies for the intended rows, secure views and functions, keep privileged credentials off clients, and test the behavior.
The key distinction: grants decide whether a database role may attempt an operation; RLS policies decide which rows that operation may access or change. You need both checks to match your design.
What RLS enforces—and what it does not
PostgreSQL evaluates policies attached to a table when a role accesses it. A policy can add a condition to the query—for example, requiring a row’s user_id to match the identity supplied by auth.uid(). Because enforcement happens in the database, it applies to access through different clients and database tools, subject to grants, bypass privileges, and other database surfaces. Supabase’s RLS guide explains the policy model and Supabase Auth helpers.
Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsA policy does not remove an existing table privilege. A role needs the relevant grant before it can perform an operation, and then an applicable policy determines which rows it may affect. Some existing Supabase projects automatically grant anon and authenticated privileges on tables in the public schema, so inspect your project rather than assuming a policy has removed access.
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Choose grants and policies for every operation
Review each exposed table by role and operation. Decide whether anon, authenticated, or another role needs to select, insert, update, or delete. Grant only the operations required, then write policies that express the allowed rows. Supabase recommends separate policies for the four operations and explicitly naming target roles with the policy’s TO clause.
| Operation | Policy condition | What to verify |
|---|---|---|
| SELECT | USING |
Which existing rows the role may read. |
| INSERT | WITH CHECK |
Whether the proposed new row is allowed. |
| UPDATE | USING and WITH CHECK |
Whether the existing row may be changed and whether the resulting row remains allowed. An applicable SELECT policy is also needed for UPDATE to work as expected. |
| DELETE | USING |
Which existing rows the role may delete. |
Example: rows owned by the current user
For an owner-only table, a common invariant is that the authenticated caller’s auth.uid() equals the row’s user_id. The insert policy should check the proposed row’s owner. For update, check both the row before the change and the new row afterward; otherwise, a user who can edit an owned row might change its user_id and transfer ownership.
This is a pattern to adapt and test, not a universal policy recipe. Consider what should happen for unauthenticated callers: auth.uid() returns null when no authenticated user is present, and an equality comparison with null does not pass. An explicit authentication check can make that intention clearer. Also assess whether JWT claims are sufficiently safe and current for each authorization decision.
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Views
Views can bypass underlying RLS by default in common configurations. With PostgreSQL 15 or later, a view can be created with security_invoker = true so that underlying policies apply to anon and authenticated callers. For older versions, Supabase advises revoking those roles’ access to the view or putting it in an unexposed schema. Check your actual PostgreSQL version and which schemas your API exposes. Supabase documents the view considerations alongside RLS.
Functions
RLS does not automatically protect function execution. Grant EXECUTE only to roles that need it, and scrutinize functions declared SECURITY DEFINER, which can run with their owner’s privileges. Supabase recommends setting their search_path to an empty value and schema-qualifying objects used inside the function. Do not place a privileged security-definer function in an exposed schema. See Supabase’s API security guidance and RLS documentation.
Columns
RLS filters rows, not individual columns. If a role must not see particular fields, consider column privileges or a separate table or view design. Supabase describes column-level privileges as an advanced control and recommends RLS combined with a dedicated table for role-specific data in common cases. Read Supabase’s column-level security guidance.
Keep privileged credentials and paths out of client code
Supabase’s service_role bypasses RLS. Secret and service-role keys must remain on the server, not in a browser or other client application. A privileged server path is not protected merely because ordinary client requests are subject to policies. Review where keys are stored and which code can use them, using Supabase’s Postgres roles guidance and secure-data guidance.
Prove the rules with tests, then check their cost
SQL that looks restrictive is not proof that the application behaves as intended. Supabase recommends keeping a SQL test file for each RLS-protected table and checking allowed and denied behavior for SELECT, INSERT, UPDATE, and DELETE under both anon and authenticated roles. For shared data, add both member and non-member cases. Run supabase test db and resolve failures before relying on the policies.
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Include negative tests: an unauthenticated request should not read or alter protected rows; an authenticated user should not access another owner’s data; and an update should not let a caller change ownership or move a row outside the permitted set. The expected results depend on your application’s rules, so make those rules explicit in the tests.
Policy filters can also affect query performance. Index columns used by policy conditions. Supabase notes that wrapping row-independent helper calls such as auth.uid() in a scalar SELECT can allow PostgreSQL to evaluate or cache the result per statement rather than for each candidate row. The effect depends on the query and policy shape; measure against your workload and inspect query plans when needed. See the RLS performance guidance.
Quick Recap
A practical review for one exposed table
- List roles and operations. Identify which roles need SELECT, INSERT, UPDATE, and DELETE access to the table.
- Inspect grants. Check current table privileges, including defaults for exposed schemas; remove operations no role should be able to attempt.
- State the row rules. Write down who may read, create, change, and delete rows, including behavior for anonymous users and shared data.
- Write operation-specific policies. Use
USINGfor rows being read, changed, or deleted;WITH CHECKfor inserted and resulting updated rows. Name intended roles explicitly. - Trace other access surfaces. Review views, function execution privileges, security-definer functions, column exposure, and any privileged server paths.
- Test allowed and denied cases. Cover each operation and relevant role, including ownership changes and shared-resource membership.
- Check performance. Index policy filter columns and inspect actual query plans under representative application queries.
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