# The app shows a blank or error page on your computer

**What you see:** `localhost:3000` is empty, white, or shows an error overlay.

**Why it happens:** Something broke while building or running the page. The details are in the browser console and in the terminal.

## How to fix it

1. Copy the error text from the page or the terminal (remove any key first).
2. Give it to your agent with the report format: what you did, expected and got.
3. If it worked a moment ago, ask to go back to the last version that worked.

## Message for your agent

```text
My app shows a blank page at localhost:3000. Read the terminal and the browser console, find the root cause, fix it, and add a test so it can't come back.
```

**How to prevent it:** Small steps with a checkpoint after each make these easy to undo.

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Source: [Agentic Makers](https://agenticmakers.app/en/help/blank-or-error-page) · License: CC BY 4.0