I have a player in one of my games that has been rolling absurdly high since the start of the campaign. I noticed fairly early on and eventually started to track their rolls for the last 4 sessions to gather evidence and found them to be nearly impossible. His "rolls" without modifiers have been as follows:

Session 6: 18 18 17 18 18 18 15 20 16 13 20 

Session 7: 17 15 18 17 16 15 18 17 16 17 15 19 14 16 16 16

Session 8: 14 16 19 12 19 18

Session 9: 18 17 14 19

He's a Bladesinger who gets 4-5 low damage attacks per turn with an excellent hit chance but low damage so the cheating has only added about 5 DPR to his output in combat, so it hasn't majorly gotten in the way for most of the campaign, but we just finished the Puzzle Cube portion of Tomb of Annihilation and his epic saving throws and ability checks have overshadowed the players' whose character's should have been better at them (Cleric Perception checks, Rogue Acrobatics checks, Paladin Athletics checks, etc.) and is starting to be a problem, we are about to enter the tomb it'self and there is going to be a lot more opportunity for the rolls to be disruptive.

So here's my plight; the player is my close friend and is rather sensitive, but is obviously cheating. One of the other party members has complained to me about it and I'd like to put it to a stop. We are playing online so I cannot just look at his dice as he rolls them or have everybody roll in the center of the table, as is standard practice in my normal games. How do I get him to stop rampantly cheating without driving him away from the game?

You've only got a couple of options here, and neither are that great.

First, use an online session-based dice rolling tool (like https://rpgsessions.com/ or https://rolz.org/). If you are already using a VTT tool (Roll20, Astral, etc) then just announce to the entire group that all die rolling will be in the tool.

This is a big change to a group. We all like rolling little pieces of plastic, and typing "/roll 2d6+4" is just not as great as picking up two d6s and dropping them in a dice tower.

You'll need some patience. Every group has a player who just can't get the hang of rolling on screen (after five Roll20 sessions, one of my players still didn't know how to roll dice). 

As a tip, do not introduce that player to macros. It only makes things worse. Just be patient, teach them over and over to type "slash r o l l space 2d20+1 enter".

The second option is to just let it go.

Talk to him as a friend. Don’t blame him, try to be as “friend to friend” as possible, but tell him some of the other guys are getting suspicious and it won’t be as fun for you if he keeps it up. Make it clear you’re helping him avoid getting booted by a group of angry players, but also that you’ll have a lot less fun personally if he continues. If your friend is a reasonable, mature friend, he should get it. If not...then you have some uncomfortable decisions ahead. But try talking first.

I look at it this way: 

There is no good reason to cheat at D&D. There is no winning and no losing. There's no point to cheating against a DM who can just invent hit points, AC, and abilities for the monster at will to counteract such cheating. If a player is going to cheat anyway, then my feeling is, maybe he just, well, needs to do it at this time. I don't question it. 

My players mostly use the VTT (Foundry in our case) to roll, but I do not require it, and I generally roll my own dice. (Hey, I paid a lot for those metal dice and the Wyrmwood dice tray with the leather lining!) If someone seemed to be rolling awfully high, I would shrug it off.

I would not suggest accusing him a cheating. He probably is, but such an accusation is going to end in misery.

On the other hand, if the other players are complaining, you can't just ignore it. I think the best way may be to just act all excited about the VTT and say you are into it and want to do all the rolls in the VTT now. (FYI, what turned my players around was the die roll animation in Foundry, and all the cool colored dice options that come with that mod.) See if you can get them excited about the VTT die rolling and this will solve your problem.

I think the first question is - how are you rolling?

There are a few low rolls in there and it does seem suss, but I know that I have one player who (using multiple dice and over different sessions) rarely rolls above a 5. Generally he can be counted on to have at least 3 nat 1's per session. Another girl (in one session) rolled 18 consistently (about 7 out of 10 times) - though that is probably a result of a novelty die being poorly balanced - not deliberate cheating but still not something you want going on. 

I understand statistics and you are probably correct, but it may just be good luck or accidentally weighted dice (ie/ weighted but he doesn't know it). Or yes, he could be cheating - just trying to give you options. 

To answer the question I use Beyond and Roll20 - and the beyond20 app to join them. I am sure with a little coding (beyond my abilities) etc it could be cheated, but most people wouldn't be bothered or able. 

You could go at it sideways if the other players are bothered by it.

"Wow dude, your rolls are on fire tonight! The XX looks like its almost dead."

You are acknowledging that he is rolling high a lot and handing the kill shot to somebody else.

The obvious solution already mentioned is switching everyone to an online tool herewith avoiding the discussion.

However as a man of principle, I wouldn't avoid the confrontation and I would call it out. The way I'd approach it is checking with the other players if they share your observation, then I would use the facts you have presented here to him and ask him if he's being fair. If he still says he's rolling fair I would tell him the others share your concern and let him propose how to take away your concerns. 

There is another explanation nobody has mentioned here:

The player might simply have bought, without realizing it, some cheap crappy dice, or heck even some expensive dice are not so great. One reason I bought metal dice is because I thought the supposedly decent plastic ones I had bought were rolling in a way that looked slightly biased to me. I watched a guy on youtube cut open his d20 and show that it was not solid inside but had some air holes off-center, and this would make it roll in a biased way. He also showed a trick which I have not been able to replicate with my plastic dice, using salt in water -- salt increases water density. You put enough salt in, supposedly the die will float, and then if you spin it, and it is unevenly weighted, the same number will keep coming up to the top. I have never gotten a plastic die to float so I can't confirm this method. And I don't feel like cutting open my dice. My point here is -- maybe he just has some crappy dice that are not weighted properly, and doesn't even realize it. This would provide the same exact type of results you are seeing.

you could have the players have a camera on the dice, then they could keep rolling physical dice, lets all be honest its way more satisfying, and you can see whether or not they're cheating

you could have the players have a camera on the dice, then they could keep rolling physical dice, lets all be honest its way more satisfying, and you can see whether or not they're cheating

I would not ever use a camera. The implicit message to all players is that you do not trust them. I would not want to send that message to my players.

It also works against human psychology. Telling someone you don't need to have a camera on them, thereby letting them know you implicitly trust them, creates an immediate obligation on the part of most people. That is, they will feel worse cheating after you told them you trusted them, than if you put a camera on them and tell them you don't trust them. We often find this with students in college. Doing all kinds of obvious tactics to prevent cheating among students only makes them try to find increasingly shrewd ways to "beat the system." If you don't put an obvious system in place to stop the cheating, some, yes, will happen, but it will (a) be obvious and easily countered, and (b) be much more infrequent, because only real cheaters will try it, and not students who just bristle at the imposition of the authority figure's draconian system.

Ultimately I would not play with people I could not trust to be honest with their rolls.

before this campaign we played through Baldur’s Gate and he’s never rolled below a 12 in over 29 sessions. That’s Has a 0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000237023766% chance of transpiring with his average of 11 rolls a session. The 12 and 13 he rolled had a +9 bonus so he still ended up rolling above a 20 on both of them, in fact no matter the bonus he’s rolled over an 18 on every check he has ever made after modifiers. (He’s also never rolled below a 21 on innovative or failed a saving throw with a dc of less than 21) so it’s absolutely not luck, I actually bought him a set of very nice metal dice for his birthday a while back From the same brand that I use so I don’t believe it’s his dice either. Thanks for laying out the options though.

Ive never actually seen the Beyond20 app, I’ll check it out! Thanks for the help.

You could go at it sideways if the other players are bothered by it.

"Wow dude, your rolls are on fire tonight! The XX looks like its almost dead."

You are acknowledging that he is rolling high a lot and handing the kill shot to somebody else.

despite his unnaturally high rolls his damage output is actually less per round that our optimized Paladin and Tempest Cleric and it hasn’t been a huge issue in combat, which is why I’ve let it carry on for so long. The problem is that now that they are going through an area of traps and tombs he’s pushing to the front and dodging all of the effects of the sinister traps by just nat 20ing any dangerous save. It takes away the need for the party to outthink and outmaneuver the majority traps and obstacles in the tomb and removes many of the interesting effects.

All right well some of this is on the DM, frankly. I don't know if that's you, OP, or someone else DMed the 29 previous sessions... But by your tally you appear to have had this going on for 2 campaigns across some 38 sessions and only now you are trying to do something about it. This should have become an issue much earlier.

I think the best bet is to use a VTT and do the rolls in-engine rather than physically. Just be enthusiastic about the rolling mechanism and how cool it is, and act like you just are into the tech rather than trying to stop a cheater.

However, if this player has been cheating this long and this extensively without being caught, I can tell you from personal experience that even being gentle and having everyone use a VTT is going to cause trouble. His character has been doing well only because of the cheating. If you stop the cheating, the player will become wildly frustrated. The cheating is happening because he can't bear to have his character be anything but perfect, and the VTT will not allow it to be perfect. That's going to make him mad, and may even result in a tantrum. Again, I've seen it happen though we were in early high school at the time. Never with an adult.

However, what did happen, that may happen to you, is when we finally stopped the cheating, that player stopped playing with us. Oh, he didn't say, "I won't play with you because you won't let me cheat anymore" but rather, we just kind of lost touch with him and he stopped coming over to play Champions (which is the primary game in which he had cheated). So be prepared for this person to stop playing with you if you find a way to successful prevent cheating.

We had a guy that similarly had "great" rolls.  But he always messed up modifiers and other things too, so, some of it may have been miscalculation.  Beyond20 saved our bacon on this one.  As we all know, rolling online isn't the most fun thing... and who wants to remember all the rules to type it up.  With Beyond20, it integrates with the majority of the VTT (Virtual Table Tops) and you just go to your character sheet on DNDBeyond and click on what you are rolling for.  Attacks?  Easy peasy... adds in all the extra modifiers.  Healing? Life Cleric?  Even adds in the hard to remember add ons at later levels.  

So instead of attacking someone that is cheating, you say that you want to make it easier for people to be able to roll and get all the modifiers they can and still use their favorite sheet manager.  And... if they want to see the dice roll and bounce around the screen... they can do that too... the number that is rolled on the dice on DNDBeyond are sent over to the VTT and show up in the calculated results.  

Everything works better with DNDBeyond and Beyond20 working together.  Not to mention, it speeds up combat, exploration and even court intrigue.  Try it today!

Quote from Grayfax >>

We had a guy that similarly had "great" rolls.  But he always messed up modifiers and other things too, so, some of it may have been miscalculation.  Beyond20 saved our bacon on this one.  As we all know, rolling online isn't the most fun thing... and who wants to remember all the rules to type it up.  With Beyond20, it integrates with the majority of the VTT (Virtual Table Tops) and you just go to your character sheet on DNDBeyond and click on what you are rolling for.  Attacks?  Easy peasy... adds in all the extra modifiers.  Healing? Life Cleric?  Even adds in the hard to remember add ons at later levels.  

So instead of attacking someone that is cheating, you say that you want to make it easier for people to be able to roll and get all the modifiers they can and still use their favorite sheet manager.  And... if they want to see the dice roll and bounce around the screen... they can do that too... the number that is rolled on the dice on DNDBeyond are sent over to the VTT and show up in the calculated results.  

Everything works better with DNDBeyond and Beyond20 working together.  Not to mention, it speeds up combat, exploration and even court intrigue.  Try it today!

 Second this. Beyond20 is amazing. Practically removes all possibility of fudging dice rolls and actually integrates DDB into a VTT (since we're still waiting on DDB to add their own VTT... Looking at you devs!).

Let all of the players know that you're implementing Beyond20 to increase gameplay speed and transparency. I'm guessing your friend isn't dumb, so they'll get the sub-context. If they refuse to download and use the Beyond20 extension then it's time to have a one-on-one chat.

I make it a point, whether in person or virtual, to never have concealed rolls. @BioWizard said it best "There is no good reason to cheat at D&D. There is no winning and no losing". D&D is a story that the players and the DM craft together. There are no main or supporting characters and every player is equally important. Having a player that consistently cheats while everyone else is playing by the rules ruins the game for everyone. Getting rid of this capability from the get-go is often times the best policy. The dice are the dice... for better or worse sometimes you just have to roll with it.

If you are worried about unbalanced plastic dice, the simple physical test is to float them in a cup of salty water. More salt will be required for heavier dice (don't even both with metal dice, although you could probably float them in oil).

Once the dice is floating, simply flick the dice and see which number comes up. If the dice is unbalanced, then it will always stop spinning with the same number on top.

Of course, some players might use this to find which dice are unbalanced to always show a 20 ;-)

I have not ever been able to get enough salt to float my plastic dice.

Remember, there is a point at which the water will be saturated and no further salt will dissolve.

The rolls shown by the OP do not indicate biased dice. If the dice was biased it might have 20 come up a lot but any ither numbers that come up more frequesntly than expected would be the faces next ot 20, which are 2, 8 and 14.

Actually the player "rolling" highly is getting 18 more often than anything else but it is next to 2, 4 and 5.

There are millions of D&D players in the world so one session with obsurdly good rolls  like that can happen (I know someone who rolled 8 6s for fireball damage which is probably about the same odds as one session like that) but for it to happen session after session is clearly cheating.

Only to-hit rolls count Nat 20s.

You can have the DC to avoid a trap be 35+. So even if he rolls a 20, he would need a +15+ in order to pass.

Lots of advice here, but for my 2 cents worth - be open with the player, not accusing but pointing out that you've noticed this pattern in his rolls, and that it's starting to look like cheating or something wrong with his dice. Like in any relationship, avoiding addressing an issue directly usually ends up with everyone feeling uncomfortable and unhappy. Talk about it, find out how your player feels. Maybe they're worried that poor dice rolls will spoil the fun, or they have some self esteem concerns about playing badly. 

It can be helpful to plan out difficult conversations before hand - work out what you want to say, and also have a a strategy for taking time out from the chat if either one of you starts to become upset - time out to clam down, but come back and deal with the issue. But don't let it fester and turn into something that can sour the friendship. 

Good luck!