EasyExperience level: 0-2 years · 3-5 years1 min read

JSON in REST APIs — Interview Questions

Reviewed by Gurusankar M.

Asked inInfosysTCSAccentureAmazon
#json#rest api#content-type#application/json#http
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Short Answer

In REST, JSON is the standard body format for both requests and responses. Clients send data as a JSON body with Content-Type: application/json (and Accept: application/json to ask for JSON back); the server parses it, does the work, and returns a JSON body plus the right status code. It's the common language between client and server.

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Concept Made Simple

Coffee Chat Question

“How is JSON used in REST APIs?”

Remember It Faster

Mind Map Answer

Request body
JSON for POST/PUT/PATCH
Response body
JSON result or error
Content-Type
application/json (what you send)
Accept
application/json (what you want back)

Learn by Doing

Hands-on Keyboard

http
POST /api/users HTTP/1.1
Content-Type: application/json
Accept: application/json

{ "name": "Guru", "email": "guru@example.com" }

HTTP/1.1 201 Created
Content-Type: application/json

{ "id": 101, "name": "Guru" }

Think Beyond the Expected

What If?

What happens if you POST JSON without a Content-Type: application/json header?

The server may not know to parse the body as JSON — many frameworks only run the JSON body parser when Content-Type is application/json, so req.body ends up empty or a raw string. Always set the header; a mismatched or missing Content-Type is a very common 'why is my body undefined?' bug.

Real World

This is the backbone of virtually every web/mobile app: the client GETs JSON to render, POSTs JSON forms, and the server returns JSON. The Content-Type/Accept headers are what make the exchange unambiguous.

Interviewer's Expectation

Keywords they're listening for:

  • JSON request & response bodies
  • Content-Type: application/json
  • Accept header
  • server parses & returns JSON
  • status code + body

Common Mistakes

  • Omitting Content-Type: application/json
  • Ignoring the Accept header
  • Returning 200 for an error with an error body

Best Practices

  • Always set Content-Type and Accept
  • Return correct status codes with JSON bodies
  • Keep request/response shapes documented

Follow-up Questions

  1. What's the difference between request and response JSON?
  2. Which status codes pair with JSON error bodies?
  3. How does content negotiation work?

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Plain-language foundations

I'm preparing for a software engineering interview and want to understand this from scratch, as a beginner.

Topic: REST APIs (JSON)
Interview question: "How is JSON used in REST APIs?"

Please:
1. Explain the core idea in simple, plain language, using an everyday analogy.
2. Define any technical terms you use.
3. Walk through one small, concrete example.
4. Finish with a single sentence I can easily remember.

Keep the tone friendly and assume I'm new to this topic.
Open inChatGPTGeminiClaude

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