API design skills
for developer jobs in 2027

APIs connect almost everything: mobile apps to back ends, services to each other, companies to payment gateways, messaging providers, logistics partners and AI models. That makes API design and integration a core skill for back-end, full-stack, integration, solutions and platform engineers — and a frequent topic in system design rounds.

These skills sit in well-paid roles. AmbitionBox shows typical back-end developer pay in India of ₹10.6–11.7 lakh in October 2026,⁷ and senior API and integration work leads to solutions architect and platform roles.

Typical back-end developer pay in India (AmbitionBox, Oct 2026)

₹10.6–11.7 lakh

Broken object-level authorisation's rank in OWASP's API Security Top 10

#1

The standard defining HTTP methods and status codes

RFC 9110

The common format for describing REST APIs

OpenAPI

Table: How API design and integration are tested (editorial summary)

Table: A sketched order API with the design decisions interviewers look for (illustrative)

Talk through the choices: versioned path, idempotent creation, cursor pagination, ownership checks on every object, a cancel action modelled as a sub-resource with a clear conflict status, and a webhook endpoint designed for duplicates.

"PUT vs PATCH?"

PUT replaces the whole resource (idempotent); PATCH applies a partial update.

"401 vs 403?"

401: not authenticated (no or invalid credentials). 403: authenticated but not allowed.

"Offset or cursor pagination?"

Offset is simple but slow and inconsistent on large, changing data; cursors are stable and efficient for feeds and big tables.

"How do you design error responses?"

Correct status code plus a consistent body: error code, message, details for field errors, and a request ID for support.

"How do you make a POST safe to retry?"

Idempotency keys stored with the result for a period; repeated requests return the stored result.

"REST, GraphQL or gRPC?"

REST for public, cacheable resource APIs; GraphQL when clients need flexible queries across related data; gRPC for fast internal service-to-service calls.

"How do you protect an API from abuse?"

Authentication, authorisation per object, input validation, rate limiting, quotas and monitoring.

"A partner's webhook arrives twice. What happens?"

Nothing bad, if you deduplicate by event ID and make processing idempotent.

Table: How API expectations have changed (editorial summary)

1. Design on paper — Write an OpenAPI spec for a small library or booking system.
2. Integrate a sandbox — Use a payment or messaging provider's sandbox with idempotency and webhooks.
3. Break your own API — Try accessing another user's resource; fix object-level authorisation.
4. Retry correctly — Add backoff with jitter and a circuit breaker around a flaky dependency.
5. Write the changelog — Make a breaking change safely with a new version and deprecation notice.

Table: Roles built on API skills and typical pay in India (AmbitionBox, October 2026; indicative)

1. Week 1: HTTP and REST — Methods, status codes, caching headers; read key parts of RFC 9110.
2. Week 2: Design — Write an OpenAPI spec with errors, pagination and versioning.
3. Week 3: Security and integration — OAuth flows, object-level authorisation, a sandbox integration with webhooks.
4. Week 4: Prove it — Take the API Design and Integration Certification.

Related tests: REST API Testing, GraphQL Fundamentals and Back-End Development. See our back-end developer guide for the wider role.

• Design reviews — agreeing resources, errors and pagination with consumers before building.
• Integrations — connecting to payment, SMS, logistics or CRM providers through their APIs and webhooks.
• Incident handling — diagnosing failures caused by timeouts, rate limits or partner changes.
• Documentation — keeping OpenAPI specs and examples accurate.
• Versioning — planning deprecations with partners and mobile app release cycles.
• Security reviews — checking authorisation and data exposure on new endpoints.

"How do you document an API well?"

An OpenAPI spec kept in sync with code, examples for every endpoint, error catalogues, authentication guides and a changelog.

"What's the difference between authentication and authorisation?"

Authentication proves who the caller is; authorisation decides what that caller may do with each resource.

• Verbs in URLs and inconsistent naming.
• 200 OK for errors.
• No authorisation per object.
• Retrying non-idempotent calls.
• Undocumented breaking changes.

Technical references are IETF RFC 9110 and RFC 6749, the OpenAPI Specification, OWASP's API Security Top 10, Stripe's idempotency documentation and Microsoft's REST API Guidelines; pay from AmbitionBox (read October 2026). Test formats and the history table are editorial summaries. Science of Apps publishes the free certification linked here. Last reviewed October 2026.

• REST — an architectural style using resources and HTTP methods.
• Idempotency key — a client-supplied ID that makes retried writes safe.
• Pagination — splitting large results into pages.
• OAuth 2.0 — a framework for delegated, scoped access with tokens.
• Webhook — an HTTP callback sent when an event happens.
• OpenAPI — a standard format for describing HTTP APIs.