Gear Rules allow for customized automation of a project's data processing. Whenever the conditions of the gear rule are met, the rule triggers a specific gear to run based on the logic set in the rule.
When any acquisition file is added or modified (including classification and metadata), all files in the acquisition will be compared to all Project Gear Rules to determine if any new gears should be run on the data in the acquisition.
One useful application of this feature is to have new data added to a project automatically processed. For example, new dicom image files in a project could trigger the dicom classifier gear. Adding classifications to a file could in turn trigger a format conversion gear like the dcm2niix gear which creates a nifti image. This new nifti image could trigger another gear to run further quality assurance gears, post-processing gears, and so on.
Another useful application is to create gear rules using SDK gears, which allow gears to access the Flywheel system in the same ways a user can. This allows automation beyond strictly curating data, including launching other gears, creating projects, creating data views, etc.
Gear Rules are unique to a Flywheel Project. New projects are created with default rules that are defined for a given site, called Gear Rule Templates, but any changes to a project Gear Rules or additional rules added are specific to that project.