Consistent labelling creates a familiar environment that the user can navigate comfortably. The more familiar the environment, the easier task of finding information.
Clear, consistent and concise labelling of controls helps users to work out the purpose of a window or dialog they have never seen before. To a visually-impaired user, clear labels are even more important. A user who relies on a screenreader has no assistance from icons, layout, or spacing to work out what the controls do, so clear labelling is essential.
Guidelines
Keep labels short. This:
Reduces the expansion of text when translated, and thus minimizes the effort required to localize the UI. Translated English text can expand up to 30% in some languages.
Facilitates the use of translation engines.
Improves speed of comprehension for the user.
Do not shorten your labels to the point of losing meaning, however. A three-word label that provides clear information is better than a one-word label that is ambiguous or vague. Try to find the fewest possible words to satisfactorily convey the meaning of your label.
Do not include text in windows that describes how to use the interface, for example You can install a new theme by dropping it here. As well as adding visual clutter, descriptive labels can also conflict with information provided in documentation.
Use standard terms. You can find a list of standard user interface terms in the GNOME Documentation Style Guide, Recommended Terminology..
Apply standard capitalization rules. See the section called “Capitalization” for guidelines about capitalization of user interface labels
A toolbar tooltip is the short description of a toolbar control's functionality that the user sees when they mouse over it.
Guidelines
Concisely state the purpose of the control. The tooltip should be more descriptive than the corresponding menu item name, if there is one, but not verbose. For example, Undo last action for the button.
Use sentence capitalization rules. See the section called “Capitalization”.
An application tooltip is the short description of your application that the user sees when they mouse over the launcher or menu item for your application. It is stored in the comment field of your application's desktop file. See the section called “Menu Item Tooltips”
Guidelines
Create short tooltips. Aim to accurately communicate the functionality of an element with the fewest words possible.
Use sentence capitalization rules. See the section called “Capitalization”.
Use standard punctuation rules, with the exception that you do not use a period to end the tooltip.
Guidelines
Use the recommended standard labels for menu items and titles, where they exist. Do not use synonyms such as the section called “Standard Menus” for a list and descriptions of standard menu items and titles.
instead of . SeeUse header capitalization rules for all menu items and titles. See the section called “Capitalization” for more information.