Minimum Security requirements for comparison

I would like to know which are the minimum security requirements for SQL Data Compare to be able to read all object defintions in a database during the comparison. I expect this to be something like a Database role for the user that logs in. I understand that system administrators and db_owners can do this, but I would like to know the minimum required.
We would like to allow developers to be able to perform comparisons, but not be able to do the synchronization. It would be nice if this can be achieved using database roles rather than server roles, as that would allow differentation for databases on the same server.