WCAG 2.1 · SC 1.4.13

Tooltip

Like toasts, there is no APG pattern — and like toasts, almost every implementation fails the same three requirements.

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The third button is icon-only, so its tooltip names it (aria-labelledby) rather than describing it. The first two already have names, so theirs describe (aria-describedby).

What to check. Hover a tooltip, then move the pointer onto the tooltip itself — it stays. Press Esc while hovering — it disappears without the pointer or focus moving. Tab to a button and the tooltip appears immediately, with no hover delay.

The three requirements

Dismissible. Esc hides it without moving the pointer or focus. A tooltip that can only be dismissed by moving away can permanently obscure the content underneath for a screen-magnifier user, who may be looking at a 4× zoom of the exact region the tooltip is covering.
Hoverable. The pointer can travel onto the tooltip and it stays. Hiding on mouseleave with no grace period fails this: the tooltip vanishes as the pointer crosses the gap, so a magnifier user can never read a tooltip longer than their viewport.
Persistent. It stays until dismissed, until hover and focus are both gone, or until it stops being valid. No auto-hide timer.

Two more that are not in 1.4.13

Never the title attribute. It cannot be styled, it appears after an uncontrollable delay, screen readers treat it inconsistently, and on touch it does not appear at all.

Never anything interactive inside. A tooltip is not focusable, so a link or button in one is unreachable by keyboard. If it needs interaction, it is a popover or a dialog — not a tooltip.

Keyboard interaction
`Tab`	Focus the trigger. The tooltip appears immediately, with no delay.
`Esc`	Dismiss, without moving the pointer or focus.

Tooltips do not exist on touch — there is no hover. Anything essential must be somewhere else as well.