API Design for System Design Interviews
High Priority20 min readUpdated October 24, 2026
AI Mock Interview
Practice this topic in a realistic system design interview
In this chapter, we'll look at how to design APIs in a system design interview. Throughout the chapter, we'll use a ticket booking system to connect the design decisions to a practical example.
1. Where API Design Fits
Most system design interviews follow a similar process:
- Clarify the requirements.
- Estimate the scale, if needed.
- Define the APIs.
- Sketch the high-level architecture.
- Dive deeper into specific components.
API design is an important part of this process because it connects the requirements to the overall architecture. It helps you define what clients can do, what information they need to provide, and what responses they should expect.
In a typical system design interview, aim to spend around 5 minutes on API design, unless the question specifically focuses on APIs.