How deep should API contract checks go before a migration?

Catalogue migrations tempt teams to duplicate every consumer path in UI automation. That rarely finishes before the cutover date. Contract checks at the shared inventory boundary usually repay the effort sooner—if you choose depth deliberately.

Shallow but honest

Assert status codes and required fields for the operations the migration will stress. Skip exhaustive schema snapshots that break on every additive, non-breaking change.

Deep where rollback hurts

If a rollback depends on inventory consistency across brands, invest in checks that prove both sides see the same stock counts under concurrent writes. Those are fewer tests, written carefully.

Environment truth

Contract suites that run against stubs only will not catch the shared-service surprise we see in readiness assessments. At least one environment must speak to the real dependency shape—even if traffic is synthetic.