I tried my hand at GMing for the first time recently and my biggest challenge was figuring out rules on the fly. I frequently found players wanted to do things that I didn't know the rules for, forcing me to choose between stopping game play to look something up or shooting from the hip making a ruling that seemed reasonable and hoping I wasn't saying something that I might have to take back later.

To be clear, I am not looking for an "out" to not do my homework. Before my session, I read through the core rule books and the pre-generated module I was using. I printed off, highlighted, and made notes on the module, monsters, and "extras" (eg. spells, abilities, skills, etc.) that I anticipated being part of the session. I even mentally ran through all the sections with the pre-generated characters and looked up the rules for all the things I would have done in the module. However when game play began, for some reason my players did not follow my script (surprise, surprise). They used skills and combat maneuvers I wasn't expecting, so I hadn't brushed up on.

How do I keep flow and balance in the game when players want to do something and I don't know the rules?

Some things I can see being helpful (but not an exclusive list):

  1. Techniques to keep play alive while rules are being researched rather than "Everyone stare at the GM while they read".
  2. Rules of thumb that can help make good rulings without looking up rules.
  3. Better ways to prepare so I will be more likely know the rules when they come up.

For the record, in this session I was playing Pathfinder, but I am hoping for more general techniques that can be applied to many different systems. If I get comfortable GMing Pathfinder and decide to try out 5e, I would like to be able to use these techniques again when new rules I don't know come up.


7 Answers 7

  1. Know the most common rules. I assume from your question that you are not making rulings about things like attack rolls and damage - but if you are, you shouldn't be. You actually need to know this stuff.

  2. The players are responsible for their characters. If what they want to do is written on their sheet then they need to know what it does. If they don't know what it does then it doesn't do anything. Allowances can and should be made for inexperienced players.

  3. Know when to look things up. There are rules you don't know and have no idea where to find them: those you make rulings on. There are rules you sort of know and could look up in 30 seconds: those you might choose to look up - or get someone else to look up while you deal with the next thing.

  4. Understand the core mechanic. Most modern RPGs have a central core mechanic (older RPGs can be a hodge-podge of mechanics). For example, D&D from 3.0 on has "roll a d20 add modifiers compare to a target number" and FFG Star Wars "Roll a bundle of dice with strange and confusing symbols and try and divine what they mean by reading them like they were chicken entrails" (I actually like this game but that is its core mechanic). If you know the core mechanic you have a skeleton to hang your rulings off that means they will "fit" the game.

  5. Determine how hard it is to do the task. Link it back to the rules you know - is it easier or harder than: hitting someone with a sword? casting a spell? running? jumping? Combine this with your core mechanic to determine what the character needs to do to succeed. For example, D&D 5e says this (DMG p. 238):

    Then ask yourself, "Is this task's difficulty easy, moderate, or hard?" If the only DCs you ever use are 10 15, and 20, your game will run just fine.

  6. Make or buy a GM screen or cheat sheet. These list out the common rules and tables etc. - it's far easier to find these on a few sheets of paper than buried in an entire book - particularly if that book was laid out by Wizards of the Coast. Making them yourself is better because by the time you make them, you won't need them because the rules will be embedded in your skull. Here are some examples.

  7. Rulings stand for the session. When you make a ruling, write it down. After the session look up the correct rules and decide if from this point forward, you will use your ruling or the "official" rules. Don't retcon things if you do decide to change.


Make rulings and fix them later.

This is the inverse of my answer here, but most d20 systems like Pathfinder and 5e give the DM ultimate authority over the game. The rules might say one thing, but if the DM says otherwise, then that's it.

Therefore, whenever you're not sure about a rule or ruling, you should go with what you think is reasonable, and have that ruling stand for the session. After the session, you can then go look up the rules and see if you were correct, and if you weren't, you can retcon the relevant part of the session.

This style helps to keep the game moving and prevents you from getting bogged down in the rules. Over time, you'll get more comfortable with the tricky parts of the rules, and you'll get a good sense of what's a reasonable ruling and what's not.

Of course, you and your players will have to accept that you might make bad rulings sometimes. However, if you talk to them about this issue ahead of time and are open to retconning bad rulings, most players should be understanding, especially if you're a new GM.

Unfortunately, DM rulings are a kind of thing that you can really only get good at through experience. One benefit of this ruling system is that you'll be able to make a lot more rulings and play a lot more than if you paused to look up rules each time you're unsure.

If you're really lost, do simulations

Sometimes, if I'm not sure how something will work out at the table, I will mentally simulate what a player would do and how I would react. This lets me predict where there might be rules issues, and, since it's not at the table, I can go look up the real rules.

For example, if I make a grapple-heavy monster, I'd think about how it would behave against the PCs, and then realize that I don't know the rules for pinning or whatever, and then go look them up.

You're not going to be able to do this for everything, but simulations will help you determine if you're walking into a rules minefield during your preparations.


Be familiar with the basic rules

One of the most important things to remember about GMing an RPG is its going to be very difficult to memorize all of the rules. A cursory flip-through of the rules system is generally enough for a new GM to be able to field themselves through basic problems they may have. If there are skill checks a good knowledge of skills is good to have. If there is combat, you should know how basic combat works from start to finish.

The rest can be fielded mostly by just utilizing the rules that you know and a little bit of common sense. For example, you don't quite remember how grapple plays out in pathfinder.. but you do remember that CMB is used to determine if its successful or not.. and you also remember that most maneuvers used without the accompanying feats provoke AOO's, And you watched a UFC match once where one guy pinned the other and started slamming him in the face with his fist so you're pretty sure it deals some kind of damage..

So use that knowledge to work your way through your rules kerfuffle.

  1. Provokes Attack of Opportunity without training (aka feats) due to counterattack from opponent
  2. Roll to grapple (?)
  3. If successful deal damage of some kind(?)
  4. Roll later on to see whether the grapple continues (?)

While you aren't too sure about most of the steps, this is actually how the grappling system works in Pathfinder. The mechanics are something you could explain just by thinking about it for a little bit. It doesn't have to be perfect. It just has to be fun. Which leads me to...

The Rule of Cool

The rules are naught but a guideline to determine how your group should go about specific challenges. A rule I would recommend picking up as a GM is the "Rule of Cool". If an action would end up in a particularly interesting result or lead to some awesome thing happening, and the person doing the action would feel good about doing something cool and it'd get your table hyped up if he actually pulled it off, it happens.. because it's cool.

The rule of cool is another example of how fun a game can be when it isn't 100% rules oriented. A monk(which is a pretty underpowered class in general) swinging off of a chandelier from the second floor of an inn and kneeing some random NPC in the face and landing it would make the person playing him feel hella awesome about themselves.

So you fudge rolls a little bit so it happens. It'll make your players happy, it'll cut down on a lot of the combat sludge, and when he rolls damage give it a little boost since he did something cool. If he fumbles, at least he can fumble coolly.


I'm going to answer this from a different perspective — as a newbie, walking this same road at the same time you are.

I am routinely in this situation as I've started running a campaign for six players of varying experience.

I set a broad goal with my players that is to be observed at all costs: minimize out-of-game "mechanic" time. This is the time when the story stops, the play is disrupted, and we are searching for rules or haggling over interpretations.

Then, I set a very specific house rule to implement this goal: when I am unclear on a mechanical rule, and nobody has an immediate insight to help move things along, I will resolve the issue at my discretion using the simplest, fairest method possible. I do this often with D&D 5e's advantage/disadvantage system. I'll often just say "eh, roll twice and take the higher/lower." This keeps the game moving. Otherwise, I'll just ballpark things like DC.

No need to be perfect.

Sometimes I've asked for a Knowledge Arcana check when I should have asked for a Religion check — well, darn. Trying to do it all perfectly will give you a very wooden, boring game that never gets into the rhythm. The rhythm is what keeps people engaged.

Our group takes breaks on the hour (give or take), and that is the time that the more OCD among us can pore over the books and get authoritative answers. When I find or am presented with an authoritative answer, I incorporate it for future use.

I think the Angry GM should be required reading for GM/DMs as well.


I would also suggest that your first adventure should be more "railroading": less options for players to diverge from the goal, more ways to learn step by step.

This is what I did for my first DMing sessions, with a free adventure I found online (worked with Pathfinder or 5E). I also clearly stated that the adventure would be of that type, and they helped in it.

This took preparation and helping tools as stated by the previous answers.


I got some really great feedback here and the feedback (particularly Dale M's answer) really helped me improve my game. There was one thing I did that no one else mentioned that I thought I would add for the next poor soul who finds themselves in this situation.

Play a short campaign and run it more than once.

I think to a certain extent, you can't avoid feeling lost the first time you GM. Being new there are a lot of "unknown unknowns" that you have no way of preparing for. The first time you play through a session, you will discover a lot of your blind spots you didn't know you had, so between sessions you can read up on them to be better prepared.

The magic happens on the second play though. This time, you will have prepared for all the places you had trouble the first time. It is like having a sneak peek at what it feels like to be an experienced GM. Different players will do different thing, so you still won't be ready for everything they do. However, since this time you were prepared for most things you can follow all the great advice in the other answers without panicking or feeling overwhelmed. It will allow you to practice deciding when to arbitrate vs look up or how to set DCs on the fly in a more low pressure setting. That practice will then make it easier when you move to a new campaign.


I have found a few basic things have stood me in good stead while running various games. If you can keep these in mind, gameplay can keep going without awkward pauses and everyone can keep having fun.

First and Foremost: The Core mechanic. Know it and understand it. This has been said in many other answers, but it absolutely bears repeating. In addition, understand that the core mechanic is really a random number generator. In a D20 based game, you are trying to balance the probability of circumstance X happening against the dice. If you come up against something unfamiliar, take a beat to consider how hard would it be to do something. if something sounds like it would be really super hard for a character to accomplish, make them roll a 19 or 20. If you think it would be easy, they only fail with a 3 or less. Use your common sense and don't take too long. This works best if you don't always tell the player what they need for success.

Second, You are the GM: Your word is final for the duration of that session. Rules lawyering is not allowed until after the session. What happens in game stays happened. No negotiation during the session. If everyone accepts this right from the start, you have less problems.

Third kinda goes with the second (with a caveat): If you are wrong about a ruling, don't be afraid to admit it, but gently remind the players that what has happened, stays happened. You might throw the players a bone by way of apology, maybe fudge the next unknown by a point or give them a juicy loot drop if it's called for.

Fourth and Most important of all, It's about the Story and Having Fun: If something doesn't make sense, but it might serve the story, give it a shot. Work some humor in there. Just don't let the games rules get in the way of of a good story and having a good time.

You can probably guess that I'm not particularly uptight about the rules in any gaming system, but that's because I don't lose sight rule 4. We are friends, and we are here to have a good time. That is the most important thing. The Game is just the excuse.


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