Context: According to the SCP Wiki, “All anomalous objects, entities, and phenomena requiring Special Containment Procedures are assigned an Object Class. An Object Class is a part of the standard SCP template and serves as a rough indicator for how difficult an object is to contain.”
Safe-class SCPs are anomalies that are easily and safely contained. Euclid-class SCPs are anomalies that require more resources to contain completely or where containment isn’t always reliable. Keter-class SCPs are anomalies that are exceedingly difficult to contain consistently or reliably, with containment procedures often being extensive and complex.