You must have a valid passport to visit Cape Verde as a US citizen. Your passport must be valid at the time of entry and have at least six months of validity beyond your planned return date. Your passport must also have at least one blank page for the entry stamp. You do not need a visa if visiting Cape Verde for less than 30 days for tourism purposes. However, for longer stays, you will need a visa, and the single-entry visa should suffice as it will allow you to visit the country for up to 90 days.