Walk me through your technical design document process and sections

WHAT THIS TESTS: Your ability to turn a vague product brief into a software design description that records design information, addresses various design concerns, and communicates that information to stakeholders. The interviewer wants to see if you treat the document as a practical tool to coordinate a large team under a single vision, not as bureaucratic overhead.

A GOOD ANSWER COVERS: Start with discovery and risk assessment before drafting anything. Then write an overview that restates goals and non-goals in engineering terms so the scope is unambiguous. Include an architecture diagram with pointers to detailed feature specifications of smaller pieces of the design. Define the data model and API contracts so the outline shows all parts of the software and how they will work. Add a rollout plan with sequencing, monitoring, and rollback criteria. Finish with success metrics tied back to the brief. Emphasize that the description needs to be a stable reference that the whole team can rely on and that it should address various design concerns ranging from performance to security.

COMMON WRONG ANSWERS: Skipping requirements clarification and jumping to tools or code is the most common mistake. Another is creating a document that only the author understands rather than serving as a communication tool for all stakeholders. Omitting non-goals, failure modes, or cross-team dependencies weakens the design. Leaving out rollout, observability, or operational concerns makes the plan untrustworthy. Treating the design as static rather than a living artifact that evolves with feedback also signals inexperience.

LIKELY FOLLOW-UPS: How do you resolve conflicting feedback from security and product? What happens when the brief changes mid-design? How do you prevent the document from becoming obsolete after launch? How do you balance completeness with a tight deadline?

ONE CONCRETE EXAMPLE: Imagine a brief for a new referral feature. You would first clarify eligibility and fraud rules with product and legal. The architecture section would show a new referrals service and its relationship to existing billing systems, acting as a pointer to detailed feature specifications of smaller pieces. The data model would define referral records and idempotency keys. The rollout plan would propose a dark launch to one percent of users with a kill switch. The metrics section would track conversion rate, fraud rate, and latency impact on checkout.