ARIA (Accessible Rich Internet Applications) is a set of attributes defined by the W3C that supplement HTML to improve the accessibility of web content and applications, especially dynamic content and advanced UI controls. ARIA helps screen readers and other assistive technologies understand the purpose, state, and behavior of UI components that aren't natively available in HTML. Without ARIA, custom widgets like tabs, modals, autocomplete fields, and dynamic content updates can be completely invisible or confusing to users with disabilities.

1. Use native HTML first – Don't use ARIA if native HTML elements can provide the semantics you need (e.g., use <button> instead of <div role="button">).
2. Don't override native semantics – Avoid changing native element semantics unless absolutely necessary.
3. All interactive ARIA controls must be keyboard accessible – Users must be able to navigate and operate them via keyboard.
4. Don't use role="presentation" or role="none" on focusable elements – These roles remove semantics, but focusable elements must remain perceivable.
5. All interactive elements must have accessible names – Use aria-label, aria-labelledby, or native labeling techniques.

aria-label provides a direct string value as the accessible name for an element (e.g., aria-label="Close dialog"). aria-labelledby references the ID(s) of other elements whose text content serves as the accessible name (e.g., aria-labelledby="title-id desc-id"). aria-labelledby takes precedence over aria-label when both are present. Use aria-labelledby when the label text already exists in the DOM; use aria-label when no visible label is present.

Use aria-hidden="true" to hide decorative or redundant content from assistive technologies while keeping it visible on screen. Common use cases include: decorative icons, duplicated content, off-screen collapsed menus, and purely visual elements. Never apply aria-hidden="true" to focusable elements or their ancestors, as this creates a confusing experience where a screen reader user can focus on an element that is "invisible" to them.

• Invalid role values – Using non-existent roles like role="dropdown" (use role="listbox" or role="menu" instead).
• Missing accessible names – Interactive elements without aria-label or aria-labelledby.
• Broken ID references – aria-labelledby or aria-controls pointing to non-existent IDs.
• aria-hidden on focusable elements – Making interactive content invisible to screen readers.
• Using ARIA when HTML is sufficient – e.g., <div role="button"> instead of <button>.
• Incorrect state attributes – Missing aria-expanded on collapsible triggers, or missing aria-selected on tabs.

ARIA landmark roles (banner, navigation, main, complementary, contentinfo, search, form, region) allow screen reader users to quickly jump between major page sections. Each landmark should be unique when possible and properly labeled using aria-label or aria-labelledby (especially when multiple landmarks of the same type exist, like multiple navigation regions). Using HTML5 semantic elements like <nav>, <main>, and <footer> automatically provides landmark roles.

aria-live informs assistive technologies about dynamic content changes so they can announce updates to the user. Values include: off (default, no announcement), polite (announces when user is idle), and assertive (announces immediately, interrupting current speech). Use aria-live="polite" for most updates (like form validation messages) and aria-live="assertive" sparingly for critical alerts. Pair with aria-atomic and aria-relevant for finer control.

Testing ARIA involves multiple approaches: Automated validators (like this tool) catch syntax errors and common mistakes. Browser DevTools (Accessibility panel in Chrome/Edge) show the computed accessibility tree. Screen reader testing with NVDA (Windows), VoiceOver (macOS), or JAWS provides real-world validation. Keyboard-only navigation testing ensures all interactive elements are reachable. Automated tools catch ~30% of issues; manual testing catches the rest. Always combine multiple testing methods.