The Compatibility Checker is a HyperCard stack from Apple which existed in facilitating a transition from System 6 to System 7.

The Compatibility Checker utility inspected every application, control panel and extension on a System 6 Mac and reported whether it would operate well under System 7.

User reports say that although the Compatibility Checker ultimately achieved its stated goals, they were confused with a myriad of messages, most of them warning them that one item or other might not function correctly under System 7.

The Compatibility Checker ignored all type and creator codes which were "????" (four question marks).