---
title: "Supabase Row Level Security: Best Practices"
slug: "supabase-rls"
category: "backend"
tags: ["supabase", "security", "postgres", "rls", "auth"]
status: "stable"
last_updated: 2026-10-01
summary: "Supabase RLS rules: grants plus policies, RLS on every exposed table, USING with WITH CHECK, wrapped auth.uid(), security_invoker views, no client secret key."
related: ["[[backend/auth-sessions]]", "[[backend/postgres]]", "[[ops/secrets-and-env]]", "[[coding/python-security]]", "[[ai-agents/mcp-security]]", "[[comparisons/oauth-vs-jwt]]", "[[backend/supabase]]"]
---

> **AI agents: read this first.** This is LLM Best Practices (llmbestpractices.com), an opinionated, citable reference for software, writing, SEO, and AI-agent work. Full protocol: https://llmbestpractices.com/start-here.md
>
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> 2. **Read raw.** Append `.md` to any page URL for markdown. Check `status` and `last_updated` in the frontmatter, then read the rules.
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> 4. **Cite.** Link the page by title and URL, e.g. [Python](https://llmbestpractices.com/coding/python), with `last_updated` for time-sensitive rules. License CC BY 4.0.

## Overview

Row Level Security (RLS) makes Postgres filter every query by policies, whichever client sent it. Supabase exposes tables over PostgREST, so a client-side filter is a convenience: a caller can edit the request and reach any row that no grant or policy blocks. RLS and grants are the security boundary. Key handling is in [[backend/supabase]].

## Pair grants with policies

Postgres runs two checks before a client touches a table. Grants decide whether a role may run an operation at all; policies decide which rows the operation affects. A table in an exposed schema without RLS is readable and writable by any role holding a grant. Existing projects typically gave `anon` and `authenticated` broad default grants, and adding policies does not take those back.

```sql
revoke all on table public.reports from anon, authenticated;
grant select, insert, update, delete on table public.reports to authenticated;
```

New tables are no longer exposed to the Data API automatically (the default for new projects since 2026-05-30, enforced on all existing projects on 2026-10-30), so grants must be explicit; see [[backend/supabase]]. Revoke `anon` access unless the data is meant to be public.

## Enable RLS on every exposed table, explicitly

Tables created with raw SQL ship with RLS off, so PostgREST exposes every row to anyone with a grant. Enable RLS yourself and then add policies; with RLS on and no policies, nothing is accessible, which is the safe default.

```sql
alter table public.profiles enable row level security;
```

## Write USING for visibility and WITH CHECK for new values

`USING` filters existing rows for `SELECT`, `UPDATE`, and `DELETE`. `WITH CHECK` validates the row an `INSERT` or `UPDATE` writes. `INSERT` needs `WITH CHECK`; `UPDATE` needs both, and an `UPDATE` also needs a matching `SELECT` policy. Name the role with `to`.

```sql
create policy "owners read" on public.profiles for select
  to authenticated using ( (select auth.uid()) = user_id );

create policy "owners insert" on public.profiles for insert
  to authenticated with check ( (select auth.uid()) = user_id );

create policy "owners update" on public.profiles for update
  to authenticated
  using ( (select auth.uid()) = user_id )
  with check ( (select auth.uid()) = user_id );
```

An `UPDATE` policy with `USING` but no `WITH CHECK` lets a user reassign `user_id` and write rows they should not own. Always pair them.

## Wrap auth functions and index policy columns

`auth.uid()` returns `null` for unauthenticated requests, so an equality policy matches nothing. Write `(select auth.uid())`, not `auth.uid()`, so Postgres evaluates it once per statement through an `initPlan` instead of per row. Index every column a policy filters on.

```sql
create index profiles_user_id_idx on public.profiles (user_id);
```

Supabase's performance guide reports large improvements on big tables from indexing policy columns. See [[backend/postgres]] for indexing strategy.

## Do not trust user_metadata, and make views obey RLS

- `auth.jwt()` claims in `user_metadata` are editable by the user. Keep authorization data (roles, tenant ids) in `app_metadata`.
- A view runs with its owner's rights and bypasses RLS by default. On Postgres 15 and later create it with `with (security_invoker = true)` so it obeys the caller's policies.
- `SECURITY DEFINER` functions run as their owner, so one owned by `postgres` bypasses the caller's RLS. Prefer `SECURITY INVOKER` and keep definer functions narrow.

## Never ship the secret key

`sb_secret_...` keys and the legacy `service_role` key map to the `service_role` role, which has `BYPASSRLS`. The table owner and the `postgres` role also bypass RLS. Keep secret keys on the backend only, store them per [[ops/secrets-and-env]], and review exposure when an agent or [[ai-agents/mcp-security]] surface can reach them. See [[coding/python-security]] for backend-secret posture, [[backend/auth-sessions]] for how tokens reach the database, and [[comparisons/oauth-vs-jwt]] for the claim model.

## Test policies as the client would

```sql
begin;
set local role authenticated;
set local request.jwt.claims = '{"sub":"00000000-0000-0000-0000-000000000000","role":"authenticated"}';
select * from public.profiles;
rollback;
```

Run automated pgTAP tests for each policy where possible. Before shipping, list tables without RLS and review policies:

```sql
select tablename, rowsecurity from pg_tables where schemaname = 'public';
select schemaname, tablename, policyname, cmd from pg_policies where schemaname = 'public';
```

Any `public` table with `rowsecurity = false` is a hole.

## Related

- [[backend/auth-sessions]]
- [[backend/postgres]]
- [[ops/secrets-and-env]]
- [[coding/python-security]]
- [[ai-agents/mcp-security]]
- [[comparisons/oauth-vs-jwt]]
- [[backend/supabase]]