secondary school academic rigor

how do colleges find out the rigor of your high school? is it solely on the application where your guidance counselor puts “very demanding” etc., or do they have access to find every available AP class at your school?

Part of the docs your GC sends includes lists/samples of the AP/IB/advanced courses. Even if a school doesn’t rank, they are asked what is the GPA of the topmost group of students – this helps those who attend schools w/grade deflation.

The school profile also includes test info, including ranges for SATs/ACT, number of students getting X AP score, etc…