API Design · Middle · Question 20 of 75

What does `304 Not Modified` save?

1Server CPU in every case
2Database writes
✓Correct answer: Bandwidth: the server confirms the client's cached version (matched by If-None-Match or If-Modified-Since) is still current and sends no body

Explanation

Generating the ETag may still require loading data; cheap ETags (version numbers, update timestamps) make it worthwhile.

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