Specification for JDWP command ReferenceType.ConstantPool says that out data contains 'count' value which is "Total number of constant pool entries", actually this command returns number of entries + 1. I think command returns value of 'constant_pool_count' item of the Class File Format, but "The value of the constant_pool_count item is equal to the number of entries in the constant_pool table plus one". So, this behavior differs from one described in specification.