What is idempotency, and which HTTP methods are idempotent?
PICTURE THIS: A REST CALL
Simple meaning
An idempotent method can be repeated with the same effect as calling it once.
WHY — HTTP instead of guessing?
Why interviewers care about HTTP:
who only read docs from people who shipped.
and tied to Full Stack work.
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:
- 1An idempotent method can
be repeated with the same effect as calling it once.
- 2GET, PUT, and DELETE
are idempotent by spec
- 3How it works
POST is not.
- 4That is why retries
are safer on GET and PUT, and why payment APIs often add idempotency keys for POST.
- 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
An idempotent method can be repeated with the same effect as calling it once. GET, PUT, and DELETE are idempotent by spec