A well system can include a completion string adjacent to a target formation and a service tool extending within the completion string. When the service tool is in an aligned position with respect to the completion string, the service tool can prevent fluid communication between the target formation and a return conduit to facilitate fluid slurry injection. In such an alignment, a reader of the service tool is positioned within a threshold distance of a tag of the completion string to receive an indicator from the tag. From the tag, the reader receives confirmation that the service tool and the completion string are properly aligned. A pulser of the service tool transmits a signal to a surface location to convey the confirmation. A user may then pump the fluid slurry through an internal fluid flow passage of the service tool to the target formation.