API Design

API design interviews evaluate contracts that are usable, evolvable, and observable across REST, GraphQL, realtime, RPC, webhooks, and quality practices—not style preferences alone.

Child sections: REST API design, GraphQL API design, realtime and streaming APIs, RPC/gRPC/tRPC, webhooks and event-driven APIs, and API quality.

On interviews: given a product feature, choose an API style, justify trade-offs, and describe versioning, errors, auth, and operational signals.

Common pitfalls: GraphQL for simple CRUD without N+1 controls, REST without idempotency for payments, realtime without reconnect semantics, and public APIs without contract tests.

Checklist:

• Match API style to clients, coupling, and scale.
• Design errors, pagination, and versioning explicitly.
• Plan auth, rate limits, and documentation together.
• Instrument APIs for SLOs and consumer breakage.