Periods
Don’t use end punctuation in headlines, headings, subheadings, UI titles, UI text, or simple lists (three or fewer words per item).
End all sentences with a period, even if they're only two words. Put one space, not two, after a period.
For information about how to use periods in bulleted lists and numbered lists, see Lists.
Headline example
Be brief—make every word count
Text example
Be brief. Make every word count.
When a phrase ending with a colon introduces a bulleted list:
If one or more list elements complete the introductory phrase preceding the colon, use a period after every list element.
If all list elements are short phrases (three words or fewer), don’t end them with periods, even if they form a complete sentence together with the list introduction.
If one or more list elements are complete sentences, use a period after every element, even if a list element contains three or fewer words.