How to make sure each person only sees their own app data

Think about an app with notes, bookings, invoices, messages, health details, customer information, or payment history. A person signs in and expects to see only their own information. If your app accidentally shows another person's records, or lets someone change or delete another account's data, the problem is not just confusion. It is a real safety failure for a multi-user app.

The simple idea comes first: every saved item must be connected to the right person, and your app must check that connection every time it shows, creates, changes, or removes data. In Supabase, the technical name is Row Level Security. Developers often shorten that to RLS. You do not need to start with the term. Start with the outcome you want: one person should stay inside their own records, not everyone else's.

Many beginners think the danger starts only when an app handles bank cards or medical data. But even a simple app can expose customer information, home addresses, phone numbers, private notes, booking times, uploaded files, or order history. If one user can see another user's information, the app feels broken immediately. If one user can edit or delete another user's records, the damage becomes even bigger because information can be changed or lost.

This is why Supabase includes row-by-row protection rules. The technical name is Row Level Security. These rules are meant to check each saved row of data and ask, in effect, does this row belong to the current person? If yes, allow it. If not, block it. That protection matters on every screen and every action, not only on the first page after sign-in. It also matters over time, because a new feature can quietly skip the rules you thought were already covering everything.

A beginner often tests the happy path: sign in, open the dashboard, and confirm it looks right. But problems often appear in the less obvious places. Maybe the list page is filtered correctly, but the edit action trusts a record number from the page. Maybe a delete button works on an item that belongs to another account. Maybe a new table was added for comments or uploaded files, but no owner link was saved with each row. In all of these cases, the app can mix data between people even though the main screen looked fine.

The practical rule is simple: every user-owned record should carry a clear owner link, usually the signed-in user's ID. Then every read, insert, update, and delete should check that owner link. The technical names are read, insert, update, and delete rules inside Row Level Security. If you use an AI builder, ask it to show those checks one by one. You are not looking for fancy wording. You are looking for proof that one person's account cannot touch another person's row.

Start with the data tables. Find every table that stores information for individual users. Confirm each row has a clear owner field. Then ask your AI builder where Supabase is enforcing row-by-row checks. After that, test with two accounts. User A should only see A's records. User B should only see B's records. Each one should only be able to create, edit, and delete their own rows. This is the fastest practical check for whether your app is respecting user boundaries.

While you are doing that review, also check where your app stores passwords, payment keys, and access codes. Those should not appear in browser-delivered files or public screens. VibeCodeWall does not look inside your private code. It checks the public app from the outside and watches for important changes over time, which helps you catch exposures that become visible after updates. That does not replace your own user-by-user data tests. It works best alongside them as a repeat habit after every app change.