Accessible Modal Dialog Patterns

Build accessible modal dialogs with focus trapping, escape dismissal, background inertness, and screen reader announcements

When to Use

• Implementing modal dialogs, confirmation prompts, or alert dialogs
• Building sheet/drawer overlays that require user attention
• Creating image lightboxes or video players in overlay
• Reviewing existing modals for keyboard and screen reader accessibility

Instructions

1. Use the native

   <dialog>

   element when possible. Modern browsers support

   <dialog>

   with

   .showModal()

   , which provides built-in focus trapping, Escape dismissal, and backdrop styling.

function Modal({ isOpen, onClose, children }: ModalProps) {
  const dialogRef = useRef<HTMLDialogElement>(null);

  useEffect(() => {
    const dialog = dialogRef.current;
    if (!dialog) return;
    if (isOpen) {
      dialog.showModal();
    } else {
      dialog.close();
    }
  }, [isOpen]);

  return (
    <dialog ref={dialogRef} onClose={onClose} aria-labelledby="dialog-title">
      {children}
    </dialog>
  );
}

2. If using a custom modal (not

   <dialog>

   ), implement all accessibility requirements manually:

function CustomModal({ isOpen, onClose, title, children }: ModalProps) {
  const modalRef = useRef<HTMLDivElement>(null);
  const triggerRef = useRef<HTMLElement | null>(null);

  useEffect(() => {
    if (isOpen) {
      triggerRef.current = document.activeElement as HTMLElement;
      // Focus the first focusable element in the modal
      requestAnimationFrame(() => {
        const firstFocusable = modalRef.current?.querySelector<HTMLElement>(
          'button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])'
        );
        firstFocusable?.focus();
      });
    }
    return () => {
      // Return focus to trigger when closing
      triggerRef.current?.focus();
    };
  }, [isOpen]);

  if (!isOpen) return null;

  return (
    <>
      <div className="backdrop" onClick={onClose} />
      <div
        ref={modalRef}
        role="dialog"
        aria-modal="true"
        aria-labelledby="dialog-title"
        onKeyDown={(e) => {
          if (e.key === 'Escape') onClose();
        }}
      >
        <h2 id="dialog-title">{title}</h2>
        {children}
      </div>
    </>
  );
}

3. Trap focus inside the modal. Tab and Shift+Tab must cycle through focusable elements within the modal only. Use a focus trap library or implement manually.

function useFocusTrap(ref: RefObject<HTMLElement>, active: boolean) {
  useEffect(() => {
    if (!active || !ref.current) return;
    const container = ref.current;

    const handleKeyDown = (e: KeyboardEvent) => {
      if (e.key !== 'Tab') return;

      const focusable = container.querySelectorAll<HTMLElement>(
        'a[href], button:not([disabled]), input:not([disabled]), select, textarea, [tabindex]:not([tabindex="-1"])'
      );
      const first = focusable[0];
      const last = focusable[focusable.length - 1];

      if (e.shiftKey && document.activeElement === first) {
        e.preventDefault();
        last.focus();
      } else if (!e.shiftKey && document.activeElement === last) {
        e.preventDefault();
        first.focus();
      }
    };

    container.addEventListener('keydown', handleKeyDown);
    return () => container.removeEventListener('keydown', handleKeyDown);
  }, [ref, active]);
}

4. Make background content inert. When the modal is open, background content must not be interactive. Use the

   inert

   attribute on the main content.

useEffect(() => {
  const main = document.getElementById('app-root');
  if (isOpen && main) {
    main.setAttribute('inert', '');
    return () => main.removeAttribute('inert');
  }
}, [isOpen]);

5. Close on Escape key press. This is expected behavior — users should never be trapped in a dialog without a keyboard exit.

6. Close on backdrop click for non-critical dialogs. For confirmation dialogs (

   role="alertdialog"

   ), require explicit button interaction.

7. Use

   role="alertdialog"

   for confirmation prompts that require the user to acknowledge or make a choice. These should not close on backdrop click.

<div
  role="alertdialog"
  aria-modal="true"
  aria-labelledby="alert-title"
  aria-describedby="alert-desc"
>
  <h2 id="alert-title">Delete Account?</h2>
  <p id="alert-desc">
    This will permanently delete your account and all data. This cannot be undone.
  </p>
  <button onClick={onCancel}>Cancel</button>
  <button onClick={onConfirm}>Delete Account</button>
</div>

8. Return focus to the trigger element when the modal closes. Save a reference to

   document.activeElement

   before opening the modal and call

   .focus()

   on it after closing.

9. Prevent body scroll when modal is open.

body.modal-open {
  overflow: hidden;
}

Details

<dialog>

<dialog>

.showModal()

::backdrop

inert

<dialog>

Focus management sequence:

1. User clicks trigger button
2. Save reference to trigger element
3. Open modal, move focus to first focusable element (or the modal container with

   tabIndex={-1}

   )
4. Trap focus within modal
5. User closes modal (Escape, close button, or backdrop click)
6. Return focus to saved trigger element

aria-modal="true"

inert

aria-modal="true"

inert

Common mistakes:

• Focus escaping the modal when Tab reaches the end (no focus trap)
• Not returning focus to trigger on close (user is lost on the page)
• Background content scrollable and interactive while modal is open
• Missing accessible name (

  aria-labelledby

  or

  aria-label

  )
• Auto-focusing a close button instead of the most relevant element

Source

https://www.w3.org/WAI/ARIA/apd/patterns/dialog-modal/

Process

1. Read the instructions and examples in this document.
2. Apply the patterns to your implementation, adapting to your specific context.
3. Verify your implementation against the details and edge cases listed above.

Harness Integration

• Type: knowledge — this skill is a reference document, not a procedural workflow.
• No tools or state — consumed as context by other skills and agents.

Success Criteria

• The patterns described in this document are applied correctly in the implementation.
• Edge cases and anti-patterns listed in this document are avoided.