API Developer Interview Prep Guide

Start with resource identification and URI design following REST conventions. Discuss HTTP methods, status codes, pagination (cursor-based for large datasets), filtering and sorting via query parameters, HATEOAS for discoverability, and versioning strategy. Address idempotency for payment endpoints and eventual consistency between inventory and order services.

GraphQL excels when clients need flexible data fetching with varying requirements, reducing over-fetching and under-fetching. Tradeoffs include increased server complexity, caching challenges compared to HTTP caching in REST, N+1 query problems requiring DataLoader patterns, and the learning curve for teams. Mention that the best architectures often use both: REST for simple CRUD and GraphQL for complex data aggregation.

Discuss token bucket or sliding window algorithms. Cover per-client limits using API keys, tiered rate limits for different subscription plans, response headers (X-RateLimit-Remaining, Retry-After), distributed rate limiting with Redis, and graceful degradation. Mention that rate limiting protects both your infrastructure and your clients from accidental abuse.

Detail your deprecation timeline, communication strategy with API consumers, sunset headers, migration guides you created, and how you monitored adoption of the new version. Show that you balanced technical idealism with practical customer impact, and quantify how many consumers you migrated successfully.

Systematic approach: check your API logs for the specific partner, analyze response time percentiles, look for correlation with traffic spikes or deployments, test the partner endpoint independently, review circuit breaker states, and examine network-level issues. Discuss implementing retry with exponential backoff, circuit breaker patterns, and better observability for integration health.

Cover OAuth 2.0 with short-lived access tokens and refresh tokens, mTLS for service-to-service communication, input validation and parameterized queries, request signing for webhook deliveries, encryption in transit and at rest, audit logging of all data access, and IP allowlisting for known partners. Mention PCI DSS compliance requirements specific to financial data.

Cursor-based pagination is the correct choice here over offset-based, which breaks with concurrent inserts and deletes. Discuss using an opaque cursor encoding the last seen ID and sort key, consistent ordering guarantees, handling deleted records, and setting appropriate page size defaults and limits. Mention how Stripe and Shopify implement cursor pagination as industry best practices.

Focus on developer experience: clear and consistent naming conventions, comprehensive documentation with runnable examples, predictable error responses with actionable messages, SDKs in multiple languages, and a sandbox environment for testing. Show that you treated the API as a product and gathered feedback from consumers to iterate on the design.