200-901 Software Development and Design Practice Question
In the context of REST API design, which HTTP status code should be returned when a client sends a request that exceeds the API rate limit?
⚠ Common exam trap
Cisco often tests the distinction between server-side errors (5xx) and client-side rate-limit errors (429), where candidates mistakenly choose 503 Service Unavailable because they confuse server overload with client rate limiting.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
429 Too Many Requests
(429 Too Many Requests) is correct because RFC 6585 defines this status code specifically for cases where a client has sent too many requests in a given time frame, exceeding the API's rate limit. REST APIs use this response to enforce throttling and inform the client to back off, often including a Retry-After header to indicate when to retry.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
503 Service Unavailable
Why it's wrong here
503 is for server-side unavailability, not client rate limiting.
- ✗
400 Bad Request
Why it's wrong here
400 means the request syntax or parameters are malformed, so the server cannot parse it. Exceeding a rate limit is a valid, well-formed request rejected on frequency grounds, which 429 Too Many Requests communicates. 400 fits invalid JSON or missing required fields.
- ✓
429 Too Many Requests
Why this is correct
429 Too Many Requests directly signals that the client has exceeded the API's rate limit, satisfying the stem's throttling constraint. Unlike 503, which indicates server unavailability, 429 specifically communicates quota exhaustion and typically accompanies a Retry-After header, letting clients back off and retry after the specified interval.
- ✗
401 Unauthorized
Why it's wrong here
401 is for missing or invalid authentication.
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