Supabase "Permission Denied for Table Users": A Plain-English Fix

You're seeing one of these errors:

new row violates row-level security policy for table "users"

permission denied for table users (code 42501)

permission denied for schema public

You paste it into the AI. The AI changes something. Now a different thing is broken. You've been going back and forth for an hour.

Let's cut through this.

What "Row Level Security" actually is

Imagine your database is a spreadsheet. Each row is a record — a user, an order, a message. Row Level Security (RLS) is a set of rules that says who is allowed to see or change which rows.

Without RLS: anyone who connects to your database can see every row. Every user's email, every order, every message. This is like leaving your filing cabinet unlocked in a public hallway.

With RLS: each person can only see their own rows. Your data is private.

The problem is that RLS has to be set up correctly, and the AI almost always gets it wrong.

The three ways the AI messes this up

1. RLS is turned off entirely

This is the most common and most dangerous one. The AI created your database tables with RLS disabled. Everything works perfectly — anyone can read and write anything. It feels fine during development. But it means any logged-in user can see every other user's data.

A security scan found that 70% of apps built with AI tools ship with RLS disabled. 170 apps were found to be actively leaking user data.

How to check: Go to your Supabase dashboard → Table Editor → click on any table → look for "RLS enabled" or "RLS disabled" at the top. If it says disabled, that's the problem.

2. RLS is on but the rules are wrong

The AI turned on RLS (good) but wrote a rule that says "let any authenticated user see all rows" instead of "let each user see only their own rows" (bad).

The difference looks like this:

Wrong (what the AI usually writes):

-- This lets ANY logged-in user see ALL data
auth.role() = 'authenticated'

Right (what it should say):

-- This lets each user see ONLY their own data
auth.uid() = user_id

One checks "are you logged in?" The other checks "is this YOUR data?" These are very different questions, and the AI consistently picks the wrong one.

3. RLS blocks the app from working at all

This is your "permission denied" error. RLS is on, but no rules were created — or the rules are so strict that the app can't do anything. It's like locking the filing cabinet and throwing away the key. Your data is safe, but you can't access it either.

How to check: Go to Supabase dashboard → Authentication → Policies. Look at the table mentioned in the error. If there are no policies, or if the policies don't match what your app is trying to do, that's the problem.

What to try

If your app is broken because of RLS, here's the order of operations:

1. Don't just turn RLS off. That will make the error go away and make your app "work" — but it means any user can see any other user's data. This is a real security vulnerability.
2. Identify which table is causing the error. The error message will say something like "for table 'users'" or "for table 'orders'." That's the table you need to fix.
3. Tell the AI exactly what to do. Don't say "fix the RLS error." Say: "Create a Supabase RLS policy for the [table name] table. Users should only be able to SELECT rows where user_id matches auth.uid(). Users should only be able to INSERT rows where user_id is set to auth.uid(). Create separate policies for SELECT, INSERT, UPDATE, and DELETE."

Being this specific is important because the AI defaults to the lazy solution (disable RLS or use the wrong check) unless you tell it exactly what you want.

Why this matters more than you think

RLS errors feel like a nuisance — just something blocking your app from working. But they're actually a security checkpoint. The error is your database telling you "someone is trying to access data they shouldn't."

The right fix isn't to remove the checkpoint. It's to set up the rules correctly so the right people get through and the wrong people don't.

This is hard to get right without understanding your data model — which tables reference which users, which operations need to be allowed, and what "this user's data" even means for each table. If your app has more than two or three tables, the rules get complex fast.