D&D (2024) Knowledge Skills - houserule idea

3.5 and 4.0 had very specific rules about identifying monsters and what you knew about them. Then 5.0 dropped all that. But I noticed 5.5 kind of indirectly brought it back with the Study action - which seems to cover that exact thing, but it costs an action. My group has been using the old rules (you get a free knowledge roll as no action when you see something) but I've never codified it for 5e. Tasha's CoE has a nice table that talks about using DC 10+CR to know things about a monster. Another non-D&D game uses the idea of breaking knowledge into three basic "buckets:" what rumors might tell you, what someone who knows about that sort of thing would know, and what an expert in that specific thing would know. And along with "passive perception," we have ideas like "passive insight" and "passive investigation" from D&D Beyond. Finally: we have the poor knowledge skills, which are oft ignored and could use some love, especially as INT becomes more of a dump-stat outside of classes that specifically use it. And while the Study action is extremely expensive in-combat - it's very cheap if you bother to scout! Putting that all together, I have an idea for how to run "what do I know about this monster" as a house rule. Constructive thoughts and suggestions welcome!

Edit: Given the discussion a few posts down about DCs and CRs, 10+CR may end up being too high. I've changed it to 1/2 CR, rounding up.

Knowledge of a Creature

You can discern information about a creature when you see one automatically for no action using your "passive knowledge," which is 10 + the appropriate knowledge skill bonus (as defined in the Study action). If you are not proficient in that skill or have disadvantage, you subtract 5; if you have advantage in that skill, add 5. (I.e. Having a +3 in arcana gives a "passive arcana" of 8 if you are not proficient, and 13 if you are.) Additionally, if you have spent at least one minute interacting with a creature or observing it, or at least one round in combat with it, you can take a Study action to discover or remember more about a creature. Once you make this check, you will need to spend another minute observing it or another round in combat with it to make another check. (CRs less than 1 are treated as 0. Otherwise, round up.)

• DC 5+1/2 CR - what rumors might tell you
• DC 10+1/2 CR - what someone who knows about that sort of thing would know
• DC 15+1/2 CR - what an expert in that specific thing would know

Example using Ice Devil, CR 14 (DCs 12, 17, 22)

• DC5+1/2 CR would get you a creature's common name ("Ice Devil") or species ("a devil"), its type ("fiend"), and probably one notable attack description, if applicable ("a spear of freezing ice!"). Very rare or unique creatures may not have commonly known types or attacks.
• DC10+1/2 CR would get you the above, plus a relative sense of its danger (a higher CR than your level would be "very strong" or "dangerous"), common types of resistances or immunities ("immune to cold and fire"), maybe some general clues as to saves ("it's fairly quick and tough"), and more specifics on the attacks or abilities ("a slowing spear of ice and a dangerous tail; some control over ice itself; it is also very perceptive and is able to shrug off many magical effects").
• DC15+1/2 CR would get you all that plus uncommon resistances and immunities ("it is also immune to poison or being poisoned"), and more specifics on the rest as you see fit (an in-game way to say that it casts Wall of Ice on recharge, it has advantage on saves vs. spells, its Dex and Wis saves are good and its Con is slightly better, killing it sends it back to Hell to reform, etc.).

Another example:

• DC 14: An adult gold dragon, known to breathe fire and make people weak with its breath!
• DC 19: A legendary creature, typically lawful good, that - like all dragons - is immune to its breath weapon type. It doesn't inspire fear like its Chromatic cousins, but it has dangerous claws all the same. They are also known to be spellcasters. They're both nimble and wise, and like all dragons, are even more powerful in their lairs.
• DC 24: Adult gold dragons are amphibious creatures that have divine spell-casting powers, including the ability to Banish creatures. They have a recharging fire breath, and a weakening breath they can use more often. Their reflexes and wit are both strong, along with their heartiness, although that is slightly less. They can also shapechange into humanoids or beasts, or even invade one's dreams, and some do this to observe humanoid society.

These examples focused on the battle-side of things, but if you have more of the lore handy that'd be great to weave in as well.

There are various things I don't like about this, but if you would like to give your 5e game a more 3e feel, this is definitely the right direction.

Knowledge skills don't get any love from me haha. If I could I would abandon them in total. I describe the world incl. monsters, if a PC might know about it due to background I tell them the information they need. I only roll on knowledge skills if there is an actual action and stake involved - which is almost never due to the nature of knowledge skills.

I follow the principle only roll if there are stakes and possible failure that is meaningful. The rogue only rolls for lockpicking if they are under time pressure while breaking in a home or fortress. If they find a locked chest somewhere in the nature - the rogue doesn't need to roll, they get the thing open.

Same applies to knowledge rolls IMO, but due to their nature they rarely are dramatic. And in general I prefer the players gathering information through roleplaying and exploring, not through a dice roll. But thats also OSR mentality speaking through me.

Additionally they feel off. For me the roll represents the random circumstances that influence our attempt to do something while the static modifier represents the actual skill and training of the character. A wizard failing their arcana check feels always so off to me. "Yeah, you studied magical beasts for years, but somehow you can't remember anything about this magical creature than the absolute basics every farmer would know". If one knows their stuff, they know. Its not like climbing a mountain where even an expert climber could fall if they have bad luck.

That all being said - If I would do knowledge checks, I would include something like your rules you present here, its a nice principle to have some sort of graded success for knowledge rolls.

I feel these are a little strong but generally like the idea. Would possibly just change it to start at the DC10+CR level (so 10, 15, 18 maybe), but also take into consideration backgrounds and class. I have a player group that are great at not meta-gaming their knowledge, so they do like asking what their character would know or observe and this is a nice matrix I could use

CRs scale too fast in comparison to skill scaling.
expertise scales +1/2 per level more or less, so expert should expect to keep up with DCs

so maybe:
5+1/2 CR
10+1/2 CR
15+1/2 CR

The OP literally describes how 3.5 handled using Knowledge: Arcana/Nature to identify monsters and magical beings. The check was DC10 + the monster's/being's HD to gain a useful piece of information. Pretty easy to 'port over to 5e

Horwath said:

CRs scale too fast in comparison to skill scaling.
expertise scales +1/2 per level more or less, so expert should expect to keep up with DCs

so maybe:
5+1/2 CR
10+1/2 CR
15+1/2 CR

Click to expand...

Thanks for the feedback! I considered this as well, for exactly the same reason. The trick is: it still remains extremely difficult for most characters, but starts to become maybe even too easy for others.

CRs eventually get up to 30 - although anything over 20-ish is exceedingly rare and typically a campaign-capstone-style monster - but CR 20 means DC 30 and that's nearly impossible without some level of specialization. Proficiency is +6 at level 20 or +12 with expertise. INT-based characters might get as high as 24 (+7), but realistically no one else is going to be over 14 (+2), and INT-based characters don't get expertise normally.

That means your typical knowledge skills are going to cluster like this at level 20:

• most characters: -1
• most characters with proficiency: +5 to +7
• wizards/artificers: +11 to +13
• rogues and bards with expertise: +12 to +14

DCs set to 1/2 CR means the upper-end of checks are around DC 20, with DC 25 being the maximum. Some characters could potentially have a "passive" knowledge that eventually auto-succeeds on even the most difficult knowledge checks. Then again: maybe that's completely fine!

I think I'll try this method and see how it seems to go. Thanks again!

andrawartha said:

I feel these are a little strong but generally like the idea. Would possibly just change it to start at the DC10+CR level (so 10, 15, 18 maybe), but also take into consideration backgrounds and class. I have a player group that are great at not meta-gaming their knowledge, so they do like asking what their character would know or observe and this is a nice matrix I could use

Click to expand...

How do you feel they are strong? One note: I don't know if most people are noticing, but lacking proficiency in a stat gives a -5 to your passive. I know it also lowers your total, but I really wanted to reward proficiency for skills that are hardly ever taken.

Certainly adding bonuses for backgrounds could work as well! If you're a soldier, maybe +2 for History, for example. Or Hermits get +2 to Nature or Religion. Sages, +2 arcana. Then again: this is also sort of rolled into the proficiency bonus options? It's also a lot to track, which makes me avoid that as a general rule, while of course exceptions are always fine.

CR shouldn't even be involved in the equation. People are more likely to know the nature and traits of a high CR red dragon than an obscure CR 1/2 monstrosity.

Base the DC on how common the creature is in stories, with a lesser contribution from how commonly it is actually encountered, and zero contribution from its CR.

I don't like characters being played like they have detailed knowledge of a creature's exact strengths and weaknesses unless there is good reason for it, because it leads to extreme metagaming and we like to emphasize story first. I know this is a perennial debate and there are various valid perspectives, with some folks prefering a much more game-ist approach, but for me this is an important issue that I don't budge on.