A rule is a single best practice. You can pick the rule or group of rules you want your code to be checked against and create a rulelist.
A rulelist is a group of rules or checks that you would like to use to measure your code against. A rulelist can have one or more rules. This is a good way to group rules that perform a particular set of checks. For example a rulelist can be created for Development activities of a project. Another rulelist can be created for Production checks or for performance etc. This enables checking different aspects of code for more insight into specific anomalies. Rulelists can be managed at site, project or user level. Site level rulelists are also referred to as Shared Rulelists. Shared rulelists are available to all projects and all users.
Each rule or best practice has a reason or area that it will impact if not followed. Undraleu refers to them as Category. Examples of Categories are: Maintainability, Readability, Supportability, Complexity etc. Each rule or best practice may belong to one or more Category. For example not following naming conventions may make the code not easy to maintain and not easy to read.
Criticality is a way of assessing the impact of violating a best practice. Undraleu allows managing the Criticality level of each rule (it can be user defined). Examples of Criticality are: Show-Stopper, Severe, Major, and Minor. By marking a best practice to one level of criticality allows a quick assessment of the code to be of a certain level of quality.
Criticality levels can drive whether the quality of the software is meeting expected standards and whether the code should promoted to production or refactored.