jetpack_sync_idc_optinAllows sites to opt in for IDC mitigation which blocks the site from syncing to WordPress.com when the home URL or site URL do not match what WordPress.com expects. The default value is either true, or the value of JETPACK_SYNC_IDC_OPTIN constant if set.
jetpack_sync_before_enqueue_{$current_filter}Modify or reject the data within an action before it is enqueued locally.
jetpack_sync_before_enqueue_{$action_name}Modify or reject the data within an action before it is enqueued locally.
jetpack_sync_prevent_sending_post_dataFilters whether to prevent sending post data to .com Passing true to the filter will prevent the post data from being sent to the WordPress.com. Instead we pass data that will still enable us to do a checksum against the Jetpacks data but will prevent us from displaying the data on in the API as well as other services.
jetpack_sync_processed_actionsAllows us to keep track of all the actions that have been sent. Allows us to calculate the progress of specific actions.
jetpack_sync_send_dataFires when data is ready to send to the server.Return false or WP_Error to abort the sync (e.g. if there’s an error) The items will be automatically re-sent later
jetpack_sync_before_send_{$item[0]}Modify the data within an action before it is serialized and sent to the server For example, during full sync this expands Post ID’s into full Post objects, so that we don’t have to serialize the whole object into the queue.
jetpack_sync_constantTells the client to sync a constant to the server
jetpack_full_sync_constantsTells the client to sync all constants to the server
jetpack_sync_remote_actionFires when an action is received from a remote Jetpack site
Jetpack Developer Resources 