unitconst finds using a untyped constant without a unit.

const duration = 5 // 5 * time.Second is correct
time.Sleep(duration)

$ go vet -vettool=`which unitconst` -unitconst.type="time.Duration" main.go
./main.go:6:13: must not use a untyped constant without a unit

The default value of unitconst.type option is time.Duration. unitconst.type accepts comma separated value such as time.Duration, unit.Length.