Alerts convey important information related to the state of your app. An alert consists of a title, an optional message, and one or more buttons. Aside from these configurable elements, the visual appearance of an alert is static and can’t be customized.
Minimize alerts. Alerts disrupt the user experience. Use alerts only for important situations like notifying people about problems. The infrequency of alerts helps ensure that people take them seriously.
For developer guidance, see UIAlertController.
Alert Titles and Messages
Write short, descriptive, multiword alert titles. The less text people have to read onscreen, the better. Try to craft a title that avoids adding extra text as a message. Because single-word titles rarely provide useful information, consider asking a question or using short sentences. Whenever possible, keep titles to a single line. Use sentence-style capitalization and appropriate punctuation for complete sentences. Don’t use ending punctuation for sentence fragments.
If you must provide a message, write short, complete sentences. Try to keep messages short enough to fit on one or two lines to prevent scrolling. Use sentence-style capitalization and appropriate punctuation.
Avoid sounding accusatory, judgmental, or insulting. People know that alerts notify them about problems and dangerous situations. As long as you use a friendly tone, it’s better to be negative and direct than positive and oblique. Avoid pronouns such as you, your, me, and my, which are sometimes interpreted as insulting or patronizing.
Avoid explaining the alert buttons. If your alert text and button titles are clear, you don't need to explain what the buttons do. In rare cases where you must provide guidance, use the word tap, preserve capitalization when referencing buttons, and don’t enclose button titles in quotes.
Generally, use two-button alerts. Two-button alerts provide an easy choice between two alternatives. Single-button alerts inform, but give no control over the situation. Alerts with three or more buttons create complexity and can require scrolling, which is a bad user experience. If you need more than two choices, consider using an action sheet instead. See Action Sheets.
Give alert buttons succinct, logical titles. The best button titles consist of one or two words that describe the result of selecting the button. Use title-style capitalization and no ending punctuation. To the extent possible, use verbs and verb phrases that relate directly to the alert title and message. Use OK for simple acceptance. Avoid using Yes and No.
Place commonly used buttons on the right and Cancel buttons on the left. Typically, buttons people are most likely to tap are on the right. Cancel buttons should always be on the left.
Label cancellation buttons appropriately. A button that cancels an alert’s action should always be labeled Cancel.
Identify destructive buttons. If an alert button results in a destructive action, such as deleting content, set the button’s style to Destructive so that it gets appropriate formatting by the system. For developer guidance, see the UIAlertActionStyleDestructive constant of UIAlertAction. Additionally, provide a Cancel button so people can safely opt out of the destructive action. Make the Cancel button bold by marking it as the default button.
Allow the Home button to cancel alerts. Tapping Home while an alert is visible exits the app. It should also produce the same effect as tapping the Cancel button—that is, the alert is dismissed without performing any action. If your alert doesn’t have a Cancel button, consider implementing a cancel action in your code that runs when the Home button is tapped.