Are there rules for "doubletalk" (i.e. a character conveying a message to allies while hiding that message from enemies)?

Question

Do the rules specify how an action like doubletalk (or something like it) works?

By "doubletalk", I am referring to a character conveying a message to allies while hiding that message from enemies. There are probable other words for it, as well.

An opposed Deception vs. Insight roll may be exactly what I am looking for, but I am looking for verification. Do the rules specify anywhere that Deception can be used in this way?

At this point, there are many campaign-specific books, so if the rules do exist, I suspect they are in one of the expansion books. I have not seen anything in any of the core books detailing rules for doubletalk.

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The reason why I am interested:

I'm asking as a DM with NPCs attempting to use coded talk in front of the party. In the moment, it was an easy decision; I had the NPCs all understand each other, and the party could roll Insight to see if they could decipher the hidden meaning. But then the players started talking about doing the same thing, and I wanted to have some way of standardizing it for them.

Deception vs. Insight for enemies could make for an interesting mechanic if there were some additional suggestion for it.

I usually find it funny in books and movies when an ally does not get the inside joke. So, having both allies and enemies roll to see if they catch the hidden meaning could be fun. Alternately, if allies and enemies have the same DC to understand the inside joke, then doubletalk becomes as harmful as it is helpful, which makes it far less useful (and less fun). So, I am hoping to find rules that may help make this mechanic a bit more enjoyable.

Specifically, might I use different DCs for allies vs. enemies?
Do allies get automatic advantage?
Or is it just safest to allow allies to auto-succeed, and this ability is only vs. enemies?

Answer 1

It was in 3.x, but not anymore

The Bluff skill from the previous edition had the exact case you're asking about:

Delivering a Secret Message
You can use Bluff to get a message across to another character without others understanding it.

However, the paradigm was shifted in 5e. You don't "use Deception" anymore. Instead, players are supposed to describe what their characters do. Now it's the DM who is in charge when determining the outcome, instead of just asking for the same opposed roll every time.

That's it — the DM uses existing described checks as models for improvising others, she doesn't need confirmation for making rulings. This is the principle known as "rulings over rules".

5th edition chooses not to explicitly codify many things. This is especially important for "doubletalk" since there're many factors involved — you and your allies might know each other well, you can share knowledge which may help to convey information, you can use gestures and cues in some situations, et cetera.

You can definitely try though

The closest thing which can be found in the 5e rules is the Thieves' Cant feature — it does exactly what you've described but is a specific class feature, not available to everyone.

While Thieves' Cant gives a guaranteed success through using a secret code, other players can always try to do the same thing using their convenient language:

The only limits to the actions you can attempt are your imagination and your character's ability scores.

When you describe an action not detailed elsewhere in the rules, the DM tells you whether that action is possible and what kind of roll you need to make, if any, to determine success or failure.

PHB p. 193

According to the rules, the DM has to determine, if the action is possible and what ability check is needed (if any). It is the DM's job as described by the source books:

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.

PHB p. 174

Questions like "what ability check is needed", "do allies get automatic advantage", etc., can't be strictly answered here, because all there things depend on the particular DM in this case.

For example, the DMG explicitly allows not using dice at all:

One approach is to use dice as rarely as possible. Some DMs use them only during combat, and determine success or failure as they like in other situations.

With this approach, the DM decides whether an action or a plan succeeds or fails based on how well the players make their case, how thorough or creative they are, or other factors.

DMG p. 236 The Role of Dice

As a player, you describe your actions or roleplay the dialog, and the DM determines the outcome, with or without an ability check.

Answer 2

Thieves' Cant

Rogues gain the class feature Thieves' Cant at 1st level:

During your rogue training you learned thieves’ cant, a secret mix of dialect, jargon, and code that allows you to hide messages in seemingly normal conversation. Only another creature that knows thieves’ cant understands such messages. It takes four times longer to convey such a message than it does to speak the same idea plainly.

In addition, you understand a set of secret signs and symbols used to convey short, simple messages, such as whether an area is dangerous or the territory of a thieves’ guild, whether loot is nearby, or whether the people in an area are easy marks or will provide a safe house for thieves on the run.

This ability is automatically acquired by any character with at least 1 level in the rogue class. You could presumably make your own in-game version.

It kind of reminds me of player advantage codes from the Knights of the Dinner Table comic, although that is more for communicating info between players without the DM catching on rather than communication between PCs.

Answer 3

Let's look at the description of the Deception skill:

Your Charisma (Deception) check determines whether you can convincingly hide the truth, either verbally or through your actions. This deception can encompass everything from misleading others through ambiguity to telling outright lies. Typical situations include trying to fast-talk a guard, con a merchant, earn money through gambling, pass yourself off in a disguise, dull someone's suspicions with false assurances, or maintain a straight face while telling a blatant lie.

The relevant phrase is "convincingly hide the truth, verbally [...] misleading others through ambiguity". That sounds an awful lot like "conveying a message to allies while hiding that message from enemies". Even if you were trying to wiggle your eyebrows or gesture towards something with a nod of your head, that would be covered by the "or through your actions" part of the skill.

On the other hand, if you are trying to point something out or gesture towards something without enemies noticing, it could involve the Sleight of Hand skill instead.

Instead of trying to list every possible thing a character can do as a skill, in 5e skills were consolidated. There is no longer 1 skill for looking at things and another for listening to things; there is just Perception. Part of 5e cutting down the amount of skills compared to older games and the "ruling over rules" philosophy means that skills are supposed to be read expansively. I'd say you are right on the money by choosing Deception vs. Insight.