Most countries’ citizens are granted a 31-day visitors' visa on arrival. You’ll need a passport with at least six months’ validity and an onward ticket. One-month extensions are granted for up to six months at T$69 per month: contact the Immigration Division, Department of Foreign Affairs & Trade.
Those intending to fly in and depart Tonga by yacht require a letter of authority from a Tongan diplomatic mission overseas or the immigration division.
You may bring two cartons of cigarettes and 2.25L of spirits or 4.5L of wine or beer into Tonga duty free.