TCP vs UDP — What's the Difference?

TCP is a connection-oriented protocol that guarantees ordered, reliable delivery of data; UDP is connectionless and sends packets without guaranteeing they arrive, arrive in order, or arrive at all.

Why they differ

• TCP's reliability guarantees come from acknowledgments and retransmission, which add latency overhead
• UDP skips those guarantees entirely, making it faster and lower-latency but requiring the application to handle any lost or out-of-order data itself

How to choose

• Use TCP for anything where correctness matters more than raw speed — web traffic (HTTP), file transfer, email
• Use UDP where speed and low latency matter more than occasional lost data — video calls, live game state, DNS lookups

FAQ

Which protocol does HTTP use?

HTTP/1.1 and HTTP/2 run over TCP. HTTP/3 is a notable exception — it runs over QUIC, which is built on UDP but adds its own reliability layer.