What is the difference between polite and assertive?

A polite region waits until the screen reader finishes its current speech before announcing the update, which suits status messages. An assertive region interrupts immediately and should be reserved for genuine, time-critical alerts such as errors, because constant interruptions are disorienting.

Does role alert need aria-live as well?

No. role alert already implies aria-live assertive and aria-atomic true, and role status implies aria-live polite. Adding a matching aria-live is harmless but redundant, and adding a conflicting one is a bug the tool flags.

What does aria-atomic control?

aria-atomic true makes the screen reader announce the entire region every time any part changes, which is right for short, self-contained messages. aria-atomic false announces only the nodes that changed, which suits a log where you want just the newest entry read.

Why should the live region exist in the DOM before it has content?

Assistive technology has to register a live region before it can watch it for changes. If you add the whole region element at the same moment you add its text, the change can be missed. Keep an empty container in the DOM on load and inject text into it later.

No. The markup is parsed in your browser using the built-in DOM parser and validated locally. Nothing you paste is sent to a server.

ARIA Live Region Debugger

Live regions are how a screen reader learns that something on the page changed without the user moving focus there, such as a form-save confirmation or a new chat message. They are also famously easy to get wrong: the wrong politeness setting, a conflicting role, or an invalid aria-relevant token can mean the announcement never happens or happens too aggressively. This tool validates your live-region markup against the ARIA spec.

How it works

The tool parses your HTML and collects every element that is a live region, either through an explicit aria-live attribute or through an implicit live role: alert, status, log, marquee or timer. For each one it checks:

aria-live is one of off, polite or assertive. An assertive value without role="alert" is flagged, because assertive interrupts the user and is usually meant only for true alerts.
Implicit roles are reconciled with any explicit aria-live. role="alert" implies assertive plus atomic, and role="status" implies polite; a conflicting explicit value is reported.
aria-atomic is true or false only.
aria-relevant contains only the tokens additions, removals, text or all, and a lone removals is flagged as noisy.
A region that is empty at load is noted as good practice, since the container should be registered before content is injected.

Example

<div aria-live="aggressive" aria-relevant="removals"></div>

This has two bugs: aggressive is not a valid aria-live value (the options are off, polite and assertive), and announcing removals alone is rarely useful. The tool reports both with the correct alternatives.

Tips and notes

Default to polite. Reserve assertive (or role="alert") for errors and other interruptions the user must hear at once.
Keep the region element in the DOM from page load and only change its text content; replacing the whole element can defeat the announcement.
For a running log, use aria-atomic="false" so only the newest line is read; for a short toast, use aria-atomic="true".
All parsing is local to your browser; the markup you paste never leaves the page.