Buy tickets for New York Staten Island ferry or is it free ?

Hi,
Should I buy a tickets for New York Staten Island ferry ? Or are the ferry tickets free ? Or are there no tickets needed ?

You don't have to buy tickets for Staten Island ferry, because it's a free service.

As it is written on their website:
The Staten Island ferry is a free service provided by the City of New York. Be aware of scammers trying to sell tickets.