You can choose to run either Utility or Analysis Gears in Project Gear Rules, but there is a restriction. Gears that use the Flywheel SDK are not available to be selected unless they have the `read-only` key added to them.
The reason for this restriction is that Gear Rules run via a System API key instead of the typical user's API key when a user starts a gear. Since the System API key doesn't have permission to write data outside of the it's container, it could fail due to permissions. By designating `read-only`, the gear is able to be used to read data but not potentially edit or overwrite any data without it being associated with a particular Flywheel user.