How does a DM define a Skill Check value?

When a DM says make a skill check, how do they decide what value they need to beat?

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Skill checks are easy, medium and hard in difficulty. Take the level, compare it to the difficulty, you get a value.

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This is of course for 4e. In 3e there were suggested DCs for each skill based on the specific task you wanted to accomplish, and the DCs were not level dependent. In 2e and earlier there wasn't really much of a skill system, but the optional skill systems provided in the book generally had you try to roll under your stat. – Lokathor Nov 4 '10 at 23:59
This answer begs the question, I think - even for DND4e. I'd like to see two thoughts addressed by those experienced with skill checks (which are pretty new to me as a formal game mechanic): 1) What is the basic math behind setting the DC (even if you use a preset table), such as "anyone unskilled can make any skill check at a XX% probability, and the difficulty should increase as a YYY-shaped curve until..." and 2) If you simplify it to easy/medium/hard, how does a DM choose between those and why/how would you adjust them? – F. Randall Farmer Nov 5 '10 at 0:52
@Randall, the article has the discussion. The second question is also mostly answered in the description. – Brian Ballsun-Stanton Nov 5 '10 at 2:23
@Brian - I didn't think so. I think I'll take Jeremiah's suggestion and post detailed questions. – F. Randall Farmer Nov 5 '10 at 3:22

This is a tough pill for a new Dungeon Master to swallow, I think. "My judgment?! I want the rules to tell me what to do!" That's understandable.

But part of the art of game mastering is learning how to make good judgments about play. D&D and similar games leave a lot of decisions about what happens to the DM. A good DM applies the following principles when deciding things:

• Consistency. The decision makes sense relative to prior decisions made with the similar parameters.
• Fairness. The decision is not biased towards any involved party.
• Believability. The decision does no violence to anyone's intuition.*
• Experience. The decision is based on knowledge from your real-world and play experience.
• Rules. The decision respects the rules used in play (written or otherwise agreed).
• Challenge. The decision does not make things too easy or too hard for the players. Obviously, this is very subjective.
• Player Happiness. The decision will be accepted by all (or at least most) of your players.

The 4E rules do give guidelines for skill checks. These are supplemented by the discussion of skill difficulties in the article Design & Development: Skill DCs (Dragon #391). This article lists easy, moderate, and hard difficulty targets by level and describes the three categories as such (excerpted):

Easy: The action involved isn’t trivial but is still pretty simple. These are the simplest checks and should represent a reasonable challenge for characters that have no training in the skill (an untrained character).

Moderate: A moderate check requires a bit of training or innate ability, or a bit of luck.

Hard: These checks are designed to test characters who are even more focused on the particular skill, though there might still be some chance of failure even for these expert characters. Without additional assistance (such as a power bonus or another character’s aid), the expert PC will succeed against these DCs around two out of three times.

While these categories still leave the DM in a position where he or she must use judgment to determine what is easy, moderate, or hard, the categories and their definitions do simplify matters. Very easy and very hard tasks naturally fall into the outer categories. It's only the challenges of middling difficulty that you need to think about.

Do you want that task to be easy? Do you want that task to be hard? Generally, if you are wondering about it, it's a moderate task. The difference between categories is +4 at the lowest levels and +8 at the highest. It's significant, but not a deal-breaker. Apply the principles I listed above and make your best decision. Keep play moving.

The players will help, too. If you make a decision that is way off, most likely the other players will check you on it. Listen to them, consider their arguments, and then reconsider your decision.

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Those links are not working now. – Zarkos Feb 12 at 5:04