Oct 08, 2026 by Offer

What is an API (Explained): Interview Answer Guide 2027

An API — Application Programming Interface — is a contract letting software components communicate without knowing each other's internals. A good api interview question answer explains REST concretely: resources at URLs, HTTP verbs (GET, POST, PUT, DELETE) as actions, status codes as results, and JSON as the message format — with one example request.

What the Api Interview Question Tests

Whether you can define an API without jargon: a contract between software, hiding implementation.
Whether you know REST mechanics: verbs, status codes, JSON payloads, statelessness.
Whether you can walk through a real example, e.g., GET /users/123 returning 200 with JSON.

How to Answer the API Interview Question

Explain the concept, then the dominant style:

The concept. An API is a contract: "call me this way, and I promise this result." It hides implementation — the client never sees the database or the algorithm.
REST, the common dialect. Resources live at URLs (`/users/123`); HTTP verbs are actions: GET reads, POST creates, PUT replaces, DELETE removes.
The conversation. Request: verb + URL + optional JSON body. Response: status code + JSON. `GET /users/123` → `200 OK` + `{"id":123,"name":"Ada"}`.
Design virtues. Stateless (each request carries its context), versioned (`/v1/`), and honest status codes instead of 200-for-everything.

Sample answer: "An API is a contract letting software interact without exposing internals. Most web APIs are REST: resources at URLs, HTTP verbs as actions, status codes as outcomes, JSON as the payload. For example, GET /users/123 returns 200 with that user's JSON."

Common Mistakes With the Api Interview Question

Defining API as 'a way to get data' only — APIs also trigger actions and hide implementation, not just serve data.
Mixing up PUT and PATCH, or using GET for state-changing operations.
Ignoring status codes: returning 200 for everything hides errors from clients.

'What is an API' filters for communication skills as much as knowledge: everyone uses APIs, but strong candidates explain the contract idea and walk a request lifecycle crisply. Have your one example rehearsed.

Keep Reading

FAQ

What is an API in simple terms?

A defined way for software to request services from other software — like a menu: you order by name without knowing how the kitchen works.

What is a REST API?

An API style using HTTP: resources have URLs, verbs (GET/POST/PUT/DELETE) say what to do, and responses carry status codes plus data, usually JSON.

What is the difference between PUT and POST?

POST typically creates a new resource; PUT replaces a resource at a known URL idempotently — repeating it has the same effect.

What are common HTTP status codes?

200 OK, 201 Created, 400 Bad Request, 401 Unauthorized, 404 Not Found, 500 Internal Server Error. Codes tell the client what happened without reading the body.

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