0Pricing
Supabase Backend as a Service · Lesson

Testing and Debugging RLS

Learn strategies for effectively testing your RLS policies to ensure they behave as expected and debug any access issues.

Testing and Debugging RLS is a free Supabase Backend as a Service lesson on CoddyKit — lesson 2 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Supabase Backend as a Service learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Why Test RLS Policies?

Row-Level Security (RLS) is powerful, but tricky. It controls who sees and modifies data directly at the database level. A small mistake can expose sensitive information or block legitimate users.

  • Security Assurance: Confirm sensitive data is protected.
  • Functionality: Ensure users can access what they need.
  • Prevent Bugs: Catch unintended access issues early.

Testing RLS is crucial for a secure and functional application.

Two Main Testing Approaches

You can test your RLS policies using two primary methods:

  • SQL Editor (Database Level): Directly interact with your database using SQL, impersonating different users. This is great for isolated testing.
  • Client-Side (Application Level): Test through your application's frontend or backend code, making authenticated API requests. This validates the entire flow.

Both methods offer unique insights into how your RLS policies behave.

Method 1: SQL Editor with SET ROLE

The most direct way to test RLS is by using the Supabase SQL Editor to impersonate a user. PostgreSQL allows you to temporarily assume the permissions of another role (user) using the SET ROLE command.

This lets you run queries as if you were that specific user, observing exactly what data they can see or modify according to your RLS policies.

SET ROLE Demo: Impersonating a User

First, enable RLS on your table. Then, create a policy. Here's how to test it in the SQL Editor. We'll use a dummy user ID for demonstration.

Note: Replace 'auth.jwt()' with your actual JWT payload if you're testing with a real user's token, or use a specific auth.uid() if you have a known user ID.

-- Assume a user with ID 'a1b2c3d4-e5f6-7890-1234-567890abcdef'
SET SESSION AUTHORIZATION 'postgres';

-- Temporarily set the auth.uid() function to return a specific ID
-- In a real scenario, this would be set by the JWT from the client
SELECT set_config('auth.request.jwt.claim.sub', 'a1b2c3d4-e5f6-7890-1234-567890abcdef', TRUE);

-- Now, run a query on a table with RLS enabled
-- For example, if you have a 'posts' table with an 'author_id' column
SELECT * FROM posts;

-- Reset session authorization
RESET SESSION AUTHORIZATION;

-- Clear the custom auth.uid() setting
SELECT set_config('auth.request.jwt.claim.sub', '', TRUE);

Verifying Access with SELECT

After setting the role or mocking the auth.uid(), you can run simple SELECT, INSERT, UPDATE, or DELETE statements to see their effect. If your RLS policy is working, you should only see (or be able to affect) the rows that the impersonated user is allowed to access.

If you see too much, or too little, your policy might need adjustment.

Method 2: Client-Side Testing

Testing RLS through your application code is crucial because it simulates real-world usage. You'll make authenticated requests using the Supabase client library (e.g., JavaScript, Python).

When a user signs in, the client library automatically includes their JWT in API requests. Supabase then uses this JWT to determine the auth.uid() and apply RLS policies accordingly.

Client-Side Demo: Authenticated Fetch

This conceptual JavaScript snippet shows how a logged-in user's session is used to fetch data. The RLS policies on the posts table will automatically filter the results based on the authenticated user.

No specific SET ROLE is needed here; it's handled by the Supabase client and backend.

import { createClient } from '@supabase/supabase-js'

const supabaseUrl = 'YOUR_SUPABASE_URL'
const supabaseAnonKey = 'YOUR_SUPABASE_ANON_KEY'

const supabase = createClient(supabaseUrl, supabaseAnonKey)

async function fetchUserPosts() {
  // Assume user is already signed in
  const { data: { user } } = await supabase.auth.getUser()

  if (user) {
    const { data, error } = await supabase
      .from('posts')
      .select('*')

    if (error) {
      console.error('Error fetching posts:', error.message)
    } else {
      console.log('User posts:', data)
    }
  } else {
    console.log('No user signed in.')
  }
}

fetchUserPosts()

Debugging RLS: EXPLAIN ANALYZE

When RLS isn't behaving as expected, EXPLAIN ANALYZE is your best friend. This SQL command shows you the execution plan of a query, including how RLS policies are applied.

Look for the "Filter" step in the plan. This indicates where your RLS policy conditions are being evaluated. It helps confirm if your policy is even being considered, and if its conditions are efficient.

EXPLAIN ANALYZE Demo

Run this in the SQL Editor (after setting the user role/ID as before) to see how RLS affects the query plan. The output will detail the query execution steps.

Examine the output for lines related to your RLS policy, often appearing as Filter: (auth.uid() = posts.user_id) or similar.

SET SESSION AUTHORIZATION 'postgres';
SELECT set_config('auth.request.jwt.claim.sub', 'a1b2c3d4-e5f6-7890-1234-567890abcdef', TRUE);

EXPLAIN ANALYZE SELECT * FROM posts WHERE id = 1;

RESET SESSION AUTHORIZATION;
SELECT set_config('auth.request.jwt.claim.sub', '', TRUE);

Common RLS Pitfalls

Debugging often involves checking for common mistakes:

  • RLS Not Enabled: Did you run ALTER TABLE your_table ENABLE ROW LEVEL SECURITY;?
  • Missing Policy: No policy means no access (unless default is permissive).
  • Incorrect USING/WITH CHECK: Conditions might not match your intent. USING for reads/updates/deletes, WITH CHECK for inserts/updates.
  • Policy Order: Multiple policies are OR'd together for access.
  • Superuser Bypass: Remember, postgres user bypasses RLS.

Test Your RLS Knowledge

You've learned about testing and debugging RLS. Let's see if you can identify the best way to verify an RLS policy's behavior for a specific user within the Supabase SQL Editor.

Recap: Testing & Debugging RLS

In this lesson, you learned how to effectively test and debug your Row-Level Security policies. We covered:

  • The importance of testing RLS for security and functionality.
  • Using the SQL Editor with SET ROLE and set_config to impersonate users.
  • Testing RLS through client-side authenticated requests.
  • Leveraging EXPLAIN ANALYZE to understand RLS policy application.
  • Identifying and resolving common RLS pitfalls.

Thorough testing ensures your data remains secure and accessible as intended!

Frequently asked questions

Is the “Testing and Debugging RLS” lesson free?

Yes — the full text of “Testing and Debugging RLS” is free to read here on the web, and the Supabase Backend as a Service course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Supabase Backend as a Service course, upgrade to CoddyKit PRO.

What will I learn in “Testing and Debugging RLS”?

Learn strategies for effectively testing your RLS policies to ensure they behave as expected and debug any access issues. You practise Supabase Backend as a Service with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Supabase Backend as a Service?

No prior experience is required. Supabase Backend as a Service on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 3, so you can start here or from the beginning and move at your own pace.

How long does the “Testing and Debugging RLS” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Supabase Backend as a Service lesson?

Yes. Every Supabase Backend as a Service lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Introduction to RLS Policies
  2. Testing and Debugging RLS
  3. Role-Based Access with RLS and Custom Claims
← Back to Supabase Backend as a Service