Availability of tooltip text for keyboard users

I am programming a desktop application and I use some icon-buttons without labels. I do not want to use Labels because of layout. So I set to every icon a descriptive tooltip text, because some icons are not self-explanatory. On mouse over the tooltip text is shown to the user.

However what about the Keyboard-only users? When they are tabbing through the application and the icon Buttons there will be no tooltip text shown. I did not found in any guideline (WCAG, ISO 9241,...) a recommandation how to implement a support for not self-explanatory icon buttons. Can anyone tell the norm? I cannot imagine that this issue has not been ruled.

I thought of some solutions:

  • showing the tooltip text on Focus, but this will be a bit irritating for the user if he knows the function of the icon button.
  • showing a context specific help pressing [F1] whil on focus.

What do you think about it? Or maybe are there some norms in the Guidelines (WCAG, ISO 9241,...)?

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