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Supabase Row Level Security (RLS) can make a query return no rows without an obvious error, while a missing SQL grant fails before any policy is checked. The reliable way to tell these apart—and catch unintended access—is to test each operation with the database role and JWT claims your app actually uses. For a repeatable baseline, write local pgTAP tests and run them with supabase test db.
Why can a Supabase query fail without an obvious error?
RLS is a row filter, not a table-level permission grant. If a role can query a table but no policy allows it to see a particular row, a SELECT may simply return an empty data array. A normal query filter that matches no rows can produce the same result. Supabase’s empty-select troubleshooting guide recommends checking the caller’s authorization context and policies as well as the query itself.
A missing SQL grant is different: PostgreSQL rejects the operation with SQLSTATE 42501 before RLS policy evaluation. Policies do not grant table privileges, and adding a policy does not remove grants already in place. Check both gates rather than trying to fix a privilege error by loosening a row predicate. Supabase explains the distinction in its Row Level Security guide.
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In Supabase, anon refers to the Postgres role used for requests without an authenticated user. A user who signs in through Supabase Auth—even an anonymous Auth user—uses the authenticated Postgres role. The public or anon API key is not itself proof that a request has a signed-in identity. Server-side code using the privileged service_role can bypass RLS, so testing only with that credential cannot prove that an ordinary user is protected.
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Policies using auth.uid() depend on the request’s JWT identity. Without an authenticated user, auth.uid() returns null; a comparison such as auth.uid() = user_id is not true for a row. Supabase’s RLS documentation covers roles, grants, and policy behavior; its testing overview calls out role and JWT claim setup as important when tests behave unexpectedly.
What should an RLS test prove?
Start with the application’s intended access, not the policy syntax. For each table, identify which roles should be able to perform each operation and which rows each identity may affect. Then test both sides of every meaningful boundary: a user who should succeed and a user who should not.
- For owner-based data, test the owner and a different authenticated user.
- For shared data, test a permitted member who is not the owner and a non-member.
- For unauthenticated access, assert the intended behavior for the
anonrole. - For privileged server workflows, test them separately from ordinary user access; do not treat a
service_rolesuccess as proof that RLS works.
Supabase recommends separate policies for SELECT, INSERT, UPDATE, and DELETE. A policy’s TO clause identifies the database role it applies to. SELECT and DELETE policies use USING to decide which existing rows are visible or targetable. INSERT uses WITH CHECK to validate the new row. UPDATE normally needs both: USING for the row before the update and WITH CHECK for the resulting row. Supabase also notes that UPDATE needs a corresponding SELECT policy to work as expected.
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For an ownership rule, include a negative update assertion: a user who may update their own row must not be able to change its user_id to claim another identity. For relationship-based access, test the actual membership conditions, not just a user who owns the record.
How to write repeatable local Supabase policy tests
- Confirm grants and RLS state. Verify RLS is enabled on the table and that SQL grants cover only the intended operations and roles. A correct policy cannot compensate for an unintended grant, and a policy alone cannot supply a missing grant.
- Define policies per operation. Use explicit roles with
TO. ApplyUSINGto existing rows for SELECT, DELETE, and the old-row side of UPDATE; applyWITH CHECKto inserted rows and the new-row side of UPDATE. Include a SELECT policy where UPDATE behavior depends on reading the target row. - Create a SQL test file. Supabase’s CLI documentation shows the
supabase test new <table>_rls.testcommand and recommends test files undersupabase/tests/, for examplesupabase/tests/profiles_rls.test.sql. See Testing and linting for the local CLI flow. - Seed realistic fixtures. Create rows for the relevant owners, members, and non-members. Set the database role and JWT claims deliberately so a test exercises the same identity-dependent policy conditions as the app. Supabase’s testing overview specifically points to
set local role authenticatedandrequest.jwt.claimswhen diagnosing test context. - Assert allowed and denied outcomes. Exercise each relevant operation as the intended role and identity. Confirm that unauthorized users cannot see, insert, update, or delete rows they should not access. Include attempts to modify protected ownership or membership fields.
- Keep the test isolated. Supabase recommends wrapping tests in a transaction and rolling back changes so fixtures do not persist. Run the suite after migrations locally and in CI.
The SQL/pgTAP path tests database behavior directly: schema, roles, policies, and rows. Client-level integration tests instead call through a Supabase client in the application’s language and exercise more of the request path. Both approaches are useful, but they localize different failures; Supabase describes them as distinct testing approaches in its testing documentation. The practical starting point for policy correctness is a repeatable database-level suite.
Run the tests with the Supabase CLI
With the local Supabase development environment running and your SQL test file in supabase/tests/, execute:
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supabase test dbThe command runs pgTAP tests against the local database. Use the suite after applying migrations so it checks the policies that the project will actually build, rather than relying on manual dashboard changes that are absent from the migration history.
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Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to diagnose common RLS failures
SELECT returns an empty array
First distinguish a query filter with no match from an RLS-filtered row. Check that the client has the expected signed-in session and JWT authorization header, then verify the policy’s TO role and predicate. If it uses auth.uid(), confirm the test or request supplies the identity the policy expects. Supabase’s troubleshooting guide describes the empty-data symptom and common causes. Disabling RLS can help isolate a diagnosis, but it is not a production fix; restore protection and correct the role, grant, or policy.
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The request returns a permission error
A SQLSTATE 42501 points to a privilege failure, not a row rejected by an RLS predicate. Check that the role has the required table grant for the operation before changing policy logic.
UPDATE succeeds in theory but changes no row
Check whether the request can see the target row under its SELECT policy, whether UPDATE’s USING condition accepts the existing row, and whether WITH CHECK accepts the resulting row. A test that asserts only that no error occurred may miss a zero-row update; assert the resulting data or affected-row behavior as well.
INSERT succeeds but the API response or upload fails
Some APIs return the inserted row. Supabase’s Storage upload troubleshooting guide documents a case where an upload’s INSERT is allowed but reading the new object metadata for the API’s RETURNING step is not. Test the insertion and the read needed to form the response; a successful insert policy alone may not cover both.
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A view seems to bypass table protection
Supabase warns that views bypass RLS by default because they are commonly created with security definer. On PostgreSQL 15 and later, security_invoker = true makes a view obey underlying RLS policies for anon and authenticated. For older PostgreSQL versions, Supabase advises revoking those roles’ access or putting the view in an unexposed schema. Verify the view’s behavior independently of direct table queries.
Keep security testing in scope
Run local policy tests against projects and data you control. Supabase’s security testing policy permits customer assessment of their own hosted project components subject to its stated limits, and prohibits cross-tenant attacks, denial-of-service testing, and request flooding. The workflow here is ordinary local development testing, not permission to probe other customers’ projects or Supabase infrastructure.
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