TCP vs UDP Tradeoffs in System Design Interviews Explained

At some point in a system design interview, this question shows up: “Would you use TCP or UDP here?” Most candidates answer confidently. Very few answer convincingly. Because the interviewer is not as

At some point in a system design interview, this question shows up: “Would you use TCP or UDP here?” Most candidates answer confidently. Very few answer convincingly. Because the interviewer is not asking about protocols. They are asking how you think under tradeoffs. --- ## Before Anything Else: This Is Not a Networking Quiz If you treat TCP vs UDP as a theory question, you miss the point. Interviewers already assume you know: * TCP is reliable * UDP is fast What they want to hear is why one breaks less than the other for a specific system. That distinction separates people who memorize from people who design. I’ve been collecting and organizing these exact interview decision points here: <a href="https://www.cracksystemdesign.com/?