Reading through the Basic Rules, there is a DC Check difficulty table found on page 58:
… but aside from the basic description of what a check is and the basic mechanics (d20 + mod/skill + any situational modifiers vs. DC) there are no guidelines for how a DM should assign DC levels to various tasks. Are there any guidelines outside of the Basic Rules that could inform 5e DMs?
In the introduction section of the Lost Mines of Phandelver there is a primer section for new DMs which includes descriptions of what type of activities would make up the Easy, Moderate, and Hard DC check levels.
- Easy (DC 10). An easy task requires a minimal level of competence or a modicum of luck to accomplish.
- Moderate (DC 15). A moderate task requires a slightly higher level of competence to accomplish. A character with a combination of natural aptitude and specialized training can accomplish a moderate task more often than not.
- Hard (DC 20). Hard tasks include any effort that is beyond the capabilities of most people without aid or exceptional ability. Even with aptitude and training, a character needs some amount of luck—or a lot of specialized training—to pull off a hard task.
