What is idempotency for PUT versus POST?
PICTURE THIS: RAG CHATBOT
Simple meaning
Repeating a PUT with the same body should leave the same final state.
WHY — API instead of guessing?
Why interviewers care about API:
contrast on API, not two memorised paragraphs.
the developer, then one case where picking wrong hurts.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Repeating a PUT with
the same body should leave the same final state.
- 2POST often creates again
unless you add an idempotency key.
- 3Payment APIs lean on
those keys.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Repeating a PUT with the same body should leave the same final state. POST often creates again unless you add an idempotency key.