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If an ability check DC is lower than your bonus, or if a check DC is higher than (20 + your bonus), and the check is a pure binary check that's pass/fail with no side effects depending on the end result of the check, is there anything in the rules that permits, discourages or denies just resolving the check without rolling?

Example:

  • DC = 5, bonus on the check = +4 → lowest possible result is 1+4, which would make the check.

  • DC = 30, bonus on the check = less than 10 → success is impossible.

Critical fails and wins (natural 1 or 20) are not included here.

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  • \$\begingroup\$ you mean if, for example, the DC is 5 and your bonus is +4, so it's impossible to fail (unless you allow crit fails)? \$\endgroup\$ – PixelMaster Apr 5 '18 at 7:18
  • \$\begingroup\$ @PixelMaster Indeed. Essentially, if a certain outcome is mathematically guaranteed, it feels weird to do an extra roll for a fixed outcome. I mean, there are already a number of answers on this site that state "only roll when there is a real consequence to failing", and if you can't fail, there isn't really a consequence to failing. \$\endgroup\$ – Nzall Apr 5 '18 at 7:24
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    \$\begingroup\$ FWIW, there's no such thing as criticals (neither fail nor success) when dealing with skill checks. At least, not in the rules - if you have crits when dealing with skill checks then it's homebrew. \$\endgroup\$ – Doc Apr 5 '18 at 15:39
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    \$\begingroup\$ As a side note, from the DM's perspective it's sometimes useful to call for rolls so the players don't know what a particular DC might be. (And if you're playing a more paranoid game, there's the ever-popular "everyone roll Perception... hmm... you don't notice anything.") \$\endgroup\$ – chrylis Apr 5 '18 at 16:17
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From p. 237 of the Dungeon Master's Guide, under the "Using Ability Scores" header:

When a player wants to do something, it’s often appropriate to let the attempt succeed without a roll or a reference to the character’s ability scores. For example, a character doesn’t normally need to make a Dexterity check to walk across an empty room or a Charisma check to order a mug of ale. Only call for a roll if there is a meaningful consequence for failure.

When deciding whether to use a roll, ask yourself two questions:

  • Is a task so easy and so free of conflict and stress that there should be no chance of failure?
  • Is a task so inappropriate or impossible — such as hitting the moon with an arrow — that it can’t work?

If the answer to both of these questions is no, some kind of roll is appropriate.

So if it's impossible to succeed no matter what or impossible to fail no matter what, and there's no difference in the consequences regardless of how well or poorly the players roll, then there's no point in calling for a roll. (There might be a point in calling for a roll if a 2 on the roll would have a worse consequence than a 17, but that'd be a separate question from this one.)

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    \$\begingroup\$ There is a difference between something that is completely impossible and something that is impossible for a particular character. Would you advocate against a roll if a particular character would be unable to do something, but another character might have a chance? What about if within the same party there are some characters that could succeed and others that would be impossible to? Would you have them all roll, or say "Rogue and barbarian, go ahead and roll. Wizard, don't bother, you won't succeed." \$\endgroup\$ – David K Apr 5 '18 at 14:04
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    \$\begingroup\$ @DavidK Kind of, except that I'd put it in in-universe terms rather than mechanical terms "Rogue, you see a branch you can hold on to; Make a dexterity check to see if you can grab it. Barbarian you can smash you fist into the wall and try to hold on that way; Make a strength check. Wizard, sorry but no - too bad you don't have feather fall, would be mighty useful right now". Similar thing for trying to move a boulder - no matter what, the bookworm of the group isn't going to do it, whereas the barbarian might be able to with some significant effort. \$\endgroup\$ – Cubic Apr 5 '18 at 15:16
  • \$\begingroup\$ great, now I'm imagining what a critical failure would look like when trying to order a mug of ale (lol!)... \$\endgroup\$ – Michael Apr 6 '18 at 18:54
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The rules state that you make an ability check when the DM calls for it. Therefore, if 1 + your bonus is higher than the DC, the DM can decide to let you auto-succeed instead. Bear in mind that if crit fails on a natural 1 are allowed (they're an optional rule), he might still have you roll.

PHB, page 173:

An ability check tests a character’s or monster’s innate talent and training in an effort to overcome a challenge. The DM calls for an ability check when a character or monster attempts an action (other than an attack) that has a chance of failure. When the outcome is uncertain, the dice determine the results.

As per RAW, a DM is not supposed to call for an ability check that cannot fail. Your DM might deviate from this rule, but unless he allows crit fails, it will just be a waste of time. Mind you - he might not know your bonuses, and unless he tells you the DC you're attempting, you won't know when you cannot fail due to bonuses. Therefore, you could be making unnecessary rolls without knowing it beforehand.


The same thing obviously goes the other way - if your bonus is not enough to make the check even if you roll a 20, then the DM probably doesn't think it's possible to succeed and shouldn't make you roll. Again, if natural 20s equal automatic success, you might still have to roll.

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