One Roll: The D20 Test

When your attempt has a real chance of failure, you make a D20 Test: roll 1d20, add an ability modifier, add your Proficiency Bonus if you're proficient, and compare the total to a target number. The 2024 revision gave this family of rolls a name because everything in the game hangs off it. The deep text is @Missing file.

The three tests

• Ability check — you attempt something; the GM names an ability and a Difficulty Class. Easy 10, moderate 15, hard 20. Skills are checks you might add proficiency to.
• Saving throw — the world attempts something on you: Dexterity to dodge the fireball, Constitution against poison, Wisdom against a charm. Your class grants proficiency in two.
• Attack roll — against a creature's Armor Class. A natural 20 always hits (and crits); a natural 1 always misses.

Advantage and disadvantage

Circumstances tip the odds: roll two d20s, take the higher with advantage, the lower with disadvantage. Sources never stack — two dice at most — and if you have both at once they cancel completely. Earning advantage before you roll is most of the tactics in the game.

Proficiency Bonus

One number, set by level — +2 at 1st to +6 at 17th — applied once per roll to what your build is trained in. @Missing file covers it, including Expertise, which doubles it.

Heroic Inspiration

When you play your character brilliantly — or when a rule grants it, as the Human's trait does every dawn — you gain Heroic Inspiration. Spend it to reroll any die you just rolled, after seeing the result, taking the new roll. You either have it or you don't; if you'd gain it while holding it, pass the spare to a teammate. Sharper than the old version, and rerolling a bad d20 after you see it changes everything: @Missing file.

The best roll

As in every edition: the one you never had to make. Describe your approach concretely — the right plan turns a hard check into no check at all.