HTTP Status Codes with JSON — Interview Questions
⚡ Short Answer
The status code carries the outcome (2xx success, 4xx client error, 5xx server error) and the JSON body carries the detail. Success bodies hold the resource; error bodies hold a consistent error shape (code, message, maybe field errors). Anti-pattern: returning 200 with {"error":...} — clients then can't rely on the status code.
☕Coffee Chat Question
Concept Made Simple
“How do HTTP status codes work together with JSON responses?”
🧠Mind Map Answer
Remember It Faster
Keep one consistent error envelope across the whole API so clients parse errors the same way everywhere.
⌨️Hands-on Keyboard
Learn by Doing
HTTP/1.1 422 Unprocessable Entity
Content-Type: application/json
{
"error": "validation_failed",
"message": "Email is invalid",
"fields": { "email": "must be a valid email" }
}🔥What If?
Think Beyond the Expected
Why is returning HTTP 200 with an error body considered a bad practice?
It breaks the contract clients, proxies, caches, and monitoring rely on. Tooling treats 2xx as success, so a 200 'error' won't trigger retries, alerts, or error handling — the failure hides. Use the correct 4xx/5xx status AND a JSON error body: the code for machines, the body for humans/details.
😂Real World
Mature APIs define one error envelope (code, message, requestId) and always pair it with the right status. Front-ends branch on res.ok/status; observability tools alert on 5xx rates — all of which relies on honest status codes.
🎯Interviewer's Expectation
Keywords they're listening for:
⚠️Common Mistakes
- ✗Returning 200 for failures
- ✗Inconsistent error shapes across endpoints
- ✗Leaking stack traces in 5xx bodies
✅Best Practices
- ✓Match status code to the real outcome
- ✓Standardize one error envelope
- ✓Return generic 5xx bodies (no internals)
🔁Follow-up Questions
- 1What's the difference between 400 and 422?
- 2How do you design a consistent error schema?
- 3Which errors should be retried by clients?
🧩Related Technologies
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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 do HTTP status codes work together with JSON responses?" 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.
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