Get all writable OIDs from snmpwalk

It's easy to do a snmpwalk to get a list of all the valid OIDs for a system. How can I tell which of those OIDs are read only, and which are writeable? $ snmpwalk -v1 -c testing 256.256.256.256 SNMPv2-MIB::sysDescr.0 = STRING: Testing Device DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (1160403) 3:13:24.03 ...