How do you design consistent, useful API error responses?
⚡ Short Answer
Use correct HTTP status codes plus a consistent machine-readable error body (RFC 7807 Problem Details: type, title, status, detail, instance, plus a stable error code and field-level validation errors). Never leak stack traces; include a correlation id for support.
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“How do you design consistent, useful API error responses?”
🧠Mind Map Answer
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{
"type": "https://api.x.com/errors/validation",
"title": "Validation failed",
"status": 400,
"code": "ORDER_INVALID",
"errors": [{ "field": "amount", "message": "must be > 0" }],
"traceId": "abc-123"
}🔥What If?
Think Beyond the Expected
Why is a stable machine-readable 'error code' better than relying on the HTTP status alone?
Many distinct failures map to the same status (400 covers dozens of validation errors). A stable code (ORDER_INVALID) lets clients branch logic and lets you change wording without breaking them — the status says the category, the code says the exact reason.
😂Real World
Inconsistent error shapes across endpoints are a top API-consumer complaint; standardizing on RFC 7807 + stable error codes + a correlation id (for log lookup) is the enterprise norm.
🎯Interviewer's Expectation
Keywords they're listening for:
⚠️Common Mistakes
- ✗Leaking stack traces / internal messages
- ✗Inconsistent error shapes per endpoint
- ✗Using 200 with an error in the body
✅Best Practices
- ✓Adopt RFC 7807 + stable error codes
- ✓Centralize mapping (@ControllerAdvice)
- ✓Always include a traceId; never leak internals
🔁Follow-up Questions
- 1How do field-level validation errors look?
- 2Why include a correlation/trace id?
- 3Where do you centralize error mapping (e.g. @ControllerAdvice)?
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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: Status Codes (REST APIs) Interview question: "How do you design consistent, useful API error 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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