For each score or segment which you defined in Toolbox, you will set a a "Target Field" where the final scores or value are set.
Image: The target field is where the score or value will show up.
You can define the field level security FLS of Toolbox Rule Set target fields any way you see fit, but keep in mind the following:
Important is that the Toolbox user who activates the Toolbox rule set must have "EDIT" access to the fields, otherwise Toolbox won't work correctly. If the user running the Rule Engine is not a System Administrator or doesn't have the Modify All Data permission, they need to ensure that the user running the Rule Engine has edit access to the target fields.
Image: Any user can define the rules, and the rule set, but the one who finally "activates" the rule set to execute the rule calculation and processing, must be a System Administrator.