How to DM D&D 5e Without Knowing All the Rules

You can DM D&D 5e without knowing all the rules if you learn four core mechanics, make a fair ruling when you get stuck and look it up after the session, and let each player own their character's rules. A one-page cheat sheet and a whiteboard for the fight cover most of what is left.

Say you work full time and run a game every few weeks, and you have read the core rules exactly once. Each session you lose minutes flipping through the Player's Handbook for a spell someone just cast. Or you prepped a haunted lighthouse for your first session and never described the lighthouse, because you spent the whole evening reading what the ghost's spells did.

You lose that time because you believe the DM has to be the one who knows the rules. You don't have to be: the players can carry a good part of them.

Which four rules cover almost everything?

You resolve nearly every situation in 5e with one of these:

• Ability check vs a DC. A player wants to do something uncertain. Pick the ability, pick a difficulty, ask for a roll: 10 is easy, 15 is a fair challenge, 20 is hard, and 25 and 30 are for the very hard and the nearly impossible (the 2024 rules' table). A natural 20 on a check is just a high roll; only an attack roll treats it as a hit. If the target is resisting, let it roll too and compare.
• Attack roll vs AC. Someone wants to hit something. Roll a d20, add the attack bonus, compare to Armor Class.
• Saving throw vs a DC. Something happens to a character and they get a chance to resist. Same anchors as checks.
• Advantage and disadvantage. Roll two d20s and keep the higher, or the lower. This replaces almost every situational modifier you might otherwise hunt for: high ground, surprise, a slippery floor.

Everything else is a special case: grappling is a check under the 2014 rules and a save under the 2024 ones, and a trap is usually a save. Before you reach for the book, ask which of the four you are looking at; most of the time that is enough.

Rule now, check later

The habit that saves the most time: handwave anything obscure that will not decide whether a character lives or dies. A player wants to climb onto a bigger creature and you cannot remember the rule, so you ask for an Athletics check against DC 15. If the ranger makes it, she is on the troll's shoulders, and if she wants to stab it in the eye from there, the answer is "sure, roll for it."

Three things keep this fair:

1. Say it out loud: "I don't remember the exact rule, so for today it works like this." Players accept rulings when they know they are rulings.
2. Stay consistent. If climbing the troll was DC 15 at noon, it is DC 15 at midnight. Write the ruling on a sticky note.
3. Look it up afterwards. The sticky notes are your homework, and you end up learning the rules your table uses, in the order they come up.

Open the book only when a character's life hangs on the outcome, or a spell sounds far too strong for its level.

If you need a minute, take it, because your players are not in a hurry. Thirty seconds of page-flipping costs nothing; what drags is thirty seconds of frozen silence while you feel bad about it.

With kids, add one more rule: when in doubt, rule in their favour. They will remember the gnome trying to lasso a griffon far longer than whether it was legal.

Share the rules load with the table

Split the job: you run the world and the monsters, the players run their characters, rules included.

Each player owns their spells and abilities, with the text ready before their turn on a card or their phone. If they cannot tell you what a spell does, they do not cast it until they can. Have them write the page number next to every spell on the sheet; when you need the book, they say the number and you are there in seconds. Hand initiative to a player too, so they keep the order and call out whose turn is next. One or two players will ignore all of this, but you only need most of the table to go along.

Younger players still own their characters; they only need help with the arithmetic. An index card with the numbers pre-added ("attack +5, damage 1d8+3, AC 16, HP 22") removes the sums that stall a turn. Hand-written spell cards help too; kids like holding something physical.

A cheat sheet for the rules this party will use

Your table needs a thin slice of the Player's Handbook: whatever this party and this session's monsters can do.

Start with the party's spells: a one-line summary for each, like fireball, 3rd level, 150 ft range, 20 ft radius, 8d6 fire, Dex save for half. For a low-level party this fits on one sheet, front and back, and grows a little with each level-up. Then do the same for whatever the cult leader can cast, before the session; reading it mid-fight is how you lose the lighthouse evening.

Add the conditions (grappled, restrained, frightened, prone), which most DM screens print; if yours does not, clip a printed sheet to it.

Last, monster cards: one index card holds the six ability modifiers, AC, HP, speed, attacks with to-hit and damage, and one line for whatever makes the creature special. If the players walk off the map, borrow a similar creature's numbers (a bear, a bandit) and add one ability; from their side of the screen it is a new monster.

Track the fight on paper

Run combat on a small whiteboard or a sheet of scrap paper:

• Write everyone in initiative order, players and monsters, with AC beneath each name.
• Under each monster, write damage taken instead of hit points left, so a player glancing over learns nothing.
• Mark conditions with something physical. A rubber band around the miniature or a coloured bead next to it saves you remembering who is concentrating.
• Pencil for hit points; in pen they are a black scribble by the third round.

Rules stick through repetition

You will not memorise the spell list by reading it. The spells your table uses stick after a few sessions because you keep seeing them. Monthly play stretches that out, so keep the notes: the sticky-note rulings, spell sheet and monster cards hold what you worked out last time.

If the full books feel like too much, Wizards of the Coast released the Essentials Kit rulebook as a free PDF in April 2020; it covers the core of play in far fewer pages. For the 2024 rules, the D&D Beyond Basic Rules are free to read online.

How to DM without knowing all the rules, on one index card

Here is the whole approach:

1. Four rules: check vs DC, attack vs AC, save vs DC, advantage or disadvantage. DCs of 10, 15 and 20.
2. Unsure of a rule: make a fair call, say it is a call, write it down, look it up after.
3. Players bring their own spell text, with page numbers on the sheet.
4. Prep only the monsters' spells and a one-line summary of the party's.
5. Whiteboard for initiative, beads for conditions, pencil for everything else.

Put it behind your screen and, next session, check the card first each time you reach for the book; most of the time the answer is on it, and the rest can wait for a sticky note.