System-agnostic modules have a hard time with difficulties for tasks.
You can write "AC: 8 or 12" and write "Atk: +4" or "HD: 8" but explaining how hard something is supposed to be can be difficult since task resolution systems vary wildly from game to game.
Some don't have them, some use d6s, some use individual mechanics, some use DCs.
Here's one you can use in any game with the 3-18 ability score spread and a class/level system.
How hard is it to get across the ledge without falling?
"Getting across the ledge is a simple Dex check for a 4th level thief"
Meaning it's a roll-equal-or-under Dex for a 4th level thief.
Thief over 4th level? +1 to your Dex for the check for each level over.
Under 4th level (any class)? -1 to your Dex for the check for each level under.
Not a thief? -5 to your check. (If it's a specialty task, -10).
"Intimidating the Lieutenant is a simple Cha check for a 6th level fighter, barbarian, paladin, etc"
"Understanding the scroll is a simple Int check for a 9th level wizard."
"Discovering the tree is hollow is a simple Wis check for a 4th level ranger or druid"
"Noticing the lance is broken is a simple Int check for a 6th level fighter, barbarian, paladin, etc"
"Eating the pies is a simple Con check for a 7th level halfling."
This seems easier for me than DCs because I usually back-engineer the DC or check modifiers from this information anyway.
I thought about using the point at which the check becomes automatic (i.e. +so much it's not worth rolling) as the baseline--like "This check is automatic for a 12th level wizard" and then you just subtract but it's harder to come up with that. (Even though it "feels" cleaner.) You find yourself figuring for who it is supposed to be a challenge and then adding numbers.
Note also that--in terms of expected success rate--there is a difference between checks based on a class prime requisite vs. those based on an unrelated score--a simple Dex check for a thief will be in the 75% success range whereas a simple thief Int check will average out lower (slightly above 50% usually).