Overlays & Surfaces
Alert / Alert Dialog
also known as alert, alertdialog
An alert dialog is a modal dialog reserved for important, often unexpected messages, errors, or confirmations that require the user to respond before continuing. It's always modal. In accessibility terms (ARIA role='alertdialog') it's used when a message demands immediate attention and has buttons to act on; a message with no buttons uses the plainer 'alert' role instead.
See it live — shadcn/ui · MUI · Ant Design
Don't confuse it with
An alert dialog is a modal dialog specifically for urgent messages needing a decision, and is always modal. A toast or banner is non-blocking status feedback with no forced response. On iOS an alert is for unexpected system issues, while an action sheet handles choices for a user-initiated action.
In the wild
'Your session has expired. Log in again?' shown by a banking app is an alert dialog.