One is the shallowest depth an index can be built to

All 3 scenarios hold

A depth of one indexes the top level only. There is nothing shallower, so anything below one is rejected rather than clamped, and the message names the depth it was given.

expected outcome broken scenario
ScenarioDepthError message?
The shallowest depth1
One below the shallowest0Index depth must be at least 1, was: 0
A negative depth-1Index depth must be at least 1, was: -1