API Design · Senior · Question 63 of 75

When does an API need explicit optimistic concurrency (ETags/`If-Match`) by default?

✓Correct answer: When several clients or users can edit the same resource and lost updates would harm data, e.g. documents, inventory, settings
2Never
3Only for GET requests

Explanation

Requiring If-Match on updates (428 if missing) makes lost updates impossible rather than unlikely.

Further reading

Test yourself

Take the API Design · Senior quiz: questions and options are shuffled, and you get a review of your mistakes at the end.

When does an API need explicit optimistic concurrency… - API Design Senior interview question