In the Tools section, the PHB says that you can disarm a trap using Thieves' Tools with a DC 15 Dexterity check.
Correct. Anyone with proficiency in Thieves' Tools can do this.
Contradicting (?) itself, the PHB also says that a Thief Rogue can, as a bonus action, disarm a trap with a Dexterity (Sleight of Hand) check using Thieves' Tools. *
This is not a contradiction, althought I understand the confusion.
A Rogue (Thief) can, as a bonus action, use thieves' tools to make a Dexterity (Sleight of Hand) check to disarm a trap.
A couple things to note:
1) If the Rogue (Thief) does not have proficiency in Sleight of Hand, and atttempt to disarm a trap using this bonus action feature, they DO NOT add their proficiency bonus.
2) They must have Thieves' Tools to attempt to disarm the trap.
There is no advantage granted here. The fact is the Dexterity (Sleight of Hand) replaces the Dexterity (Thieves' tools) check which would be normally made BECAUSE it is being done as a bonus action. Hence the feature name:
Fast Hands.
You never grant advantage for doubling-down on a skill and tool unless they are directly related. Sleight of Hands
normally is only used for picking pockets, concealing an object, and legerdemain. This is a special case use that replaces the proficiency bonus normally granted by Thieves' tools, in which all rogues are proficient.
Contradicting (?) the PHB, the DMG simply does not mention Thieves' Tools in the Traps section at all. Neither as a general rule (for comparison, the 2014 DMG said you might call for "a Dexterity check using thieves' tools to perform the necessary sabotage"), nor in any of the sample traps. One sample trap can be disarmed with a DC 15 Dexterity (Sleight of Hand) check, no tools mentioned. And all the rest are handled narratively once detected, e.g. cut the trip wire (explicitly no ability check required), deface the glyph, or wedge a spike under the pressure plate.
So what's the RAW here? What's the RAI, even?
Whether or not Thieves' tools are needed would depend very much on the nature of the trap:
Referencing the Examples Traps in the DMG I get the problem. The trap game system is poorly designed (big shock!). Once you know of the trap, apparently iron spikes handle 80% of the problems LOL!
As to the Poisoned Needle. Again,
any PC can attempt THIS trap via Dexterity (Sleight of Hand), such as a Bard which would likely have Sleight of Hand proficiency.
A Rogue, however, can use Dexterity (Thieves' tools) to disarm the same trap, or any of the other traps if something like the iron spikes isn't available as a simple counter-measure.
Where WotC's design falls apart is there is NO check of any sort required in employing the iron spike solution in the DMG. On the other side, a rogue attempting a Dexeterity (Thieves' tools) would risk possibly setting off the trap if they failed the DC 15 (if such a thing is still possibly in 2024...).
Are we supposed to handle disarming traps narratively? If yes, WHY does it say that you can roll Thieves' Tools to disarm traps? Are we supposed to roll Thieves' Tools? Then WHY doesn't it mention them in the DMG at all? Are we supposed to do both, or either, or DM's choice? Then WHY doesn't it specify that?
It is always DM's choice and it doesn't specify anything because WotC doesn't really carry out on the "good" design concepts in 5E. Even at the end of traps the tell you that you can build your own and offer a table, but show an actual
example of this process??? OH, NO!!!
Consider how often in the example traps iron spikes can disarm them once the trigger mechanism is detected, and no checks are required. Then why even have checks for Rogues to disarm traps if 80+% don't even need Thieves' tools but just iron spikes?
* Important note: the entire Tools section in the PHB lists abilities, not skills, but elsewhere skills ARE specified. E.g. it says that picking locks is a Dexterity check using Thieves' Tools, but if you go to "Lock" in the glossary, it says it's a Dexterity (Sleight of Hand) check with Thieves' Tools. Musical Instruments is listed as a Charisma check, but I mean, it's a Performance check. So it's possible they meant that using Thieves' Tools is always a Dexterity (Sleight of Hand) check, and just neglected to write it down anywhere.
Tools should be disassociated from skills. Sleight of Hand proficiency does not enable you to pick a lock, proficiency in the tools needed to pick the lock is what lets you add proficiency. Performance is not for playing an instrument, but should be for dancing, etc. where there is not an applicable tool proficiency (e.g. instrument).
Don't say "if you have both you get advantage". You need one or the other, not both. Both is bad design IMO.
For example, there is no herbalism skill, there is an herbalism kit. Proficiency in Nature shouldn't make you better at knowning how to use something (the herblism kit) you
already know how to use.
I feel your pain. It is why 2024 is not the new year for a new edition of D&D for me. It's a pity, really, as the 50th anniversary, and I would love to corner the WotC designers in a room and make them answer for these poor design choices.