Terms of service are reviewed by contributors and divided into small points that we can discuss, compare and ultimately assign a score with a badge:
+ Good, - Mediocre, × Alert, or → Informative.

Once a service has enough badges to assess the fairness of their terms for users, a class is assigned automatically by pondering the average scores.

Class A are the best terms of services: they treat you fairly, respect your rights and will not abuse your data.

Class B  The terms of services are fair towards the user but they could be improved.

Class C  The terms of service are okay but some issues need your consideration.

Class D  The terms of service are very uneven or there are some important issues that need your attention.

Class E  The terms of service raise very serious concerns.

No Class Yet  We haven't sufficiently reviewed the terms yet.

Right now, you will notice that not many services have a class assigned. That is because we need more data and more reviews before we can start assigning them. Moreover, we are still experimenting with how to apply classes.

More from the blog: Why so many services have "No Class Yet"