Most tooltip libraries are overkill if you just want a small label on hover. A data-tooltip attribute and a sprinkle of CSS gets the job done.

<button data-tooltip="Save changes">Save</button>
[data-tooltip] {
  position: relative;
}
[data-tooltip]::after {
  content: attr(data-tooltip);
  position: absolute;
  bottom: 100%;
  left: 50%;
  transform: translateX(-50%) translateY(-4px);
  padding: 0.25rem 0.5rem;
  background: #222;
  color: #fff;
  font-size: 0.75rem;
  border-radius: 4px;
  white-space: nowrap;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.15s ease;
}
[data-tooltip]:hover::after,
[data-tooltip]:focus::after {
  opacity: 1;
}

Result


For accessibility, prefer real aria-label attributes when the button has no visible text. The data-tooltip is a visual nicety, not a replacement for proper labels.