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"headline": "API Design Advanced Interview Guide",
"description": "Deep-dive API design interview prep \u2014 REST constraints, resource naming, idempotency, versioning strategies, pagination, GraphQL vs REST tradeoffs.",
"datePublished": "2026-03-20",
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"@type": "Organization",
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"@type": "FAQPage",
"mainEntity": [
{
"@type": "Question",
"name": "What is the difference between REST, GraphQL, and gRPC and when should you use each?",
"acceptedAnswer": {
"@type": "Answer",
"text": "REST is the standard for public APIs — universally understood, caches naturally over HTTP, works with any HTTP client, and simple to document. Choose REST for external developer APIs. GraphQL solves overfetching and underfetching problems — ideal for mobile clients and situations where multiple clients (web, mobile, tablet) need different data shapes from the same API. The tradeoff is GraphQL's N+1 query problem and more complex caching. gRPC uses Protocol Buffers for binary serialization and HTTP/2 for transport, giving 3-10x better performance than REST/JSON. Choose gRPC for internal microservice communication where latency and throughput matter — not for public APIs or browser clients, which cannot call gRPC directly without workarounds."
}
},
{
"@type": "Question",
"name": "What API versioning strategies are most common and which should I recommend in interviews?",
"acceptedAnswer": {
"@type": "Answer",
"text": "The three main API versioning strategies are: URL path versioning (/api/v1/users) — most common in practice, used by Stripe, GitHub, and Twitter; explicit, cacheable, works with any client, but creates parallel URL namespaces. Header versioning (API-Version: 2) — cleaner URLs but harder to test, requires header support, and complicates caching with Vary headers. Query parameter versioning (/users?version=2) — easy to add but easy to forget and breaks caching. In interviews, recommend URL path versioning for public APIs because it is explicit and universally compatible. Header versioning is acceptable for internal APIs where you control all clients. Always have a deprecation strategy: Deprecation and Sunset headers, minimum 6-month sunset windows for public APIs."
}
},
{
"@type": "Question",
"name": "What is the difference between offset pagination and cursor pagination?",
"acceptedAnswer": {
"@type": "Answer",
"text": "Offset pagination (GET /users?limit=20&offset=100) is simple but has a critical performance problem: SQL OFFSET scans and discards all skipped rows, making deep pages catastrophically slow on large tables. It also suffers from consistency issues when records are inserted or deleted between page requests. Cursor pagination (GET /users?limit=20&after=opaquecursor) uses a WHERE clause against an indexed column (e.g., WHERE id > lastid), giving O(log n) performance regardless of page depth. It is consistent against concurrent mutations. The tradeoff: cursor pagination cannot jump to arbitrary page numbers or display 'showing 221-240 of 4,521.' Use cursor pagination for large datasets and infinite scroll; use offset pagination only for small, static datasets where total count display is required."
}
},
{
"@type": "Question",
"name": "What is idempotency and how do idempotency keys work?",
"acceptedAnswer": {
"@type": "Answer",
"text": "Idempotency means an operation produces the same result whether executed once or multiple times. GET, PUT, and DELETE are naturally idempotent. POST is not — submitting a payment form twice creates two charges. Idempotency keys solve this for POST: the client generates a unique UUID and includes it in the request header (Idempotency-Key: 550e8400-...). The server checks whether it has seen this key before — if yes, it returns the stored response without re-executing the operation; if no, it processes the request and stores the response keyed by the idempotency key. Stripe's implementation is the reference model. Keys should expire (24 hours is common for payments) and the stored response should include the full request hash to detect if a client retries with a different body for the same key."
}
}
]
}