Mock Drift: Mockoon vs Contract Mocks

Short answer: A mock drifts when it is maintained separately from the API. A contract mock is generated from the spec, so it cannot return a shape the contract does not declare. The first is a copy that goes stale; the second is a rendering of the source.

How drift shows up

The mock returns a field the API removed, misses a new field, or keeps an old type. The client develops against the mock and fails against the real service.

What a contract mock keeps

Condition	Separate mock	Contract mock
Removed field	May remain	Not present
New field	May be missed	From spec
Type change	May be stale	Current
Response shape	As maintained	Valid

Why the source matters

A generated mock is a build output, like generated code, so it is current on every save. A separate mock is a copy that needs a process to stay aligned.

The honest takeaway

For a stable surface, a separate mock is fine. For a moving API, the drift is the cost that generation removes.

This is part of the Powerduck vs Mockoon comparison. Next, read the CLI comparison.