The System Design Interview Rubric Strong Candidates Internalize
The core checkpoints interviewers grade in senior system design rounds, from requirements and estimates to data, reliability, and trade-offs.
A strong answer is a chain of defended choices
Interviewers are not only checking whether you know common components. They are checking whether your choices follow from the product constraints. A strong answer sounds like a chain: requirement, estimate, architecture choice, trade-off, failure mode, mitigation.
The checkpoint categories
Most system design rounds can be graded against a stable set of categories. The exact prompt changes, but the interviewer is usually listening for the same underlying evidence.
- Requirements and scope: core features, non-goals, users, and success metrics.
- Capacity and estimation: QPS, storage, bandwidth, growth, and peak traffic.
- API and data model: contracts, entities, indexes, ownership, and consistency.
- Architecture: services, queues, caches, storage, boundaries, and request flows.
- Reliability and scale: failure modes, backpressure, retries, replication, and recovery.
- Trade-offs: why this design is right for the stated constraints and not just fashionable.
How to use the rubric while answering
Do not mechanically recite every category. Use the rubric as a mental coverage map. If the prompt is a chat system, real-time delivery and reliability deserve more time. If it is a URL shortener, key generation, storage, cache behavior, and abuse controls matter more.
The goal is to make the interviewer confident that your design is not accidental. Every major component should have a reason, a scale assumption, and a known failure mode.