Normally, I don’t really have to deal with rules at a detailed level. As the DM, everything in the rulebooks and subsequent clarifications from the authors are still just guidelines, and I can make a call and run with it. Similarly, when I play in other people’s games, I try really hard to rein in my inner rules lawyer. Unless the DM asks what the rule is or a given ruling legitimately seems to be a mistake (it happens to all of us!), it just doesn’t come up for me.
In organized play like Adventurers League, however, the situation changes a little. For the sake of parity, adhering to RAW matters. When a situation arose recently in which a character not proficient with Thieves’ Tools wanted to attempt to pick a lock, I ruled that the character would be unable to succeed. The player accepted the ruling and contacted me privately later to discuss – which I greatly appreciated! He didn’t bog the game down, and the discussion was friendly and open. When rules questions do arise, that’s how we should do it. But because the game in question occurs under the auspices of the AL, I needed to make certain I hadn’t misunderstood the rule.
This question has come up before and I found an extensively-researched answer on the Role-Playing Games Stack Exchange. The answer linked to a lot of research in the books, plus this tweet by Mike Mearls shortly after 5e’s release:
Let’s look at the actual rules in the text, which admittedly have a bit of ambiguity. The Lock description reads:
Without the key, a creature proficient with thieves’ tools can pick this lock with a successful DC 15 Dexterity check. (PHB 152)
For context, Jeremy Crawford – the actual arbiter of rules questions at Wizards of the Coast – discussed this specific text:
Two pages later, in the Thieves’ Tools section, we have the following text which in my opinion creates the real ambiguity:
Proficiency with these tools lets you add your proficiency bonus to any ability checks you make to… open locks. (PHB 154)
I read it as saying that you need this tool proficiency to add your bonus whenever you do attempt it – but it doesn’t explicitly state either way.
The rule on “Working Together” implies that lockpicking requires proficiency:
A character can only provide help if the task is one that he or she could attempt alone. For example, trying to open a lock requires proficiency with thieves’ tools, so a character who lacks that proficiency can’t help another character in that task. (PHB 175, emphasis mine)
The DMG, which came out after Mearls’ tweet but before Crawford’s, matches that last rule. Under “Locked Doors”:
Characters who don’t have the key to a locked door can pick the lock with a successful Dexterity check (doing so requires thieves’ tools and proficiency in their use). (DMG 103, emphasis mine)
The current version of the Sage Advice compendium (v1.14, from 2016) does not address thieves’ tools or locks at all.
Based on the balance of the rules, I have therefore chosen (for now) to go with the texts as the authoritative source: “you can certainly try” but it won’t succeed. This protects the role of rogues and other folks who plan ahead to make sure they have this proficiency. Adventurers can, of course, employ other methods to deal with locks, just as my group dealt with the one in question using a (successful) Strength check.
At some point, Wizards might issue a formal errata correction, which would obviously take precedence. I’d appreciate it either way for the purposes of organized play. If they do, I’ll update this post.