Static mock servers are useful. I would not tell anyone to skip them if all they need is quick contract validation or a temporary frontend stand-in. The trouble starts when the integration depends on previous calls, mutable resources, or webhook-driven transitions.
Use a mock server when
- you mainly need example responses
- your frontend team needs a temporary stand-in
- state does not materially affect the workflow
Use a stateful sandbox when
- create -> read -> update sequences matter
- your app reacts to webhooks or retries
- you need realistic scenario testing, not just static payloads
That line matters. We are not trying to replace every mock server. We are talking about the point where a team realizes “the mock is technically fine, but it still is not helping us test the thing that actually breaks.”