Techniques are disclosed for implementing custom object-in-memory formats in a data grid network appliance. The techniques include maintaining a record of format definitions on a client device of the data grid and a corresponding record of format definitions on a server device of the data grid. Each format definition may indicate one or more attributes of an object class and data types and byte ranges of the attributes. The client device may serialize one or more objects for storage in the data grid based on respective format definitions associated with the one or more objects and retrieved from the record of format definitions maintained on the client device. Further, the server device may perform one or more data grid operations using format definitions retrieved from the record of format definitions maintained on the server device.