I know there's a by the book definition that goes like it's a mix of jargon and all that. How it takes four times as long to convey that message as it would normally. But what does that mean? Is it like, you just put a whole sentence as a sort of puzzle where you take certain words to form a phrase? A bunch of slang terms like "Let's shiv the fancies, take their yellows, and throw them in a stew" that's a mix of knowledge of the area, and terms that would only make sense to thieves? Or do you just say your character is using thieves' cant? Is there a difference between the spoken and written versions? Am I asking too many questions? Honestly, I'm just curious what y'all think thieves' cant would actually sound like and want to see an IC use of thieves' cant and then an OOC explanation.

And yes, I'm just too lazy to do the research. :p

Edit: Just want to know just for fun's sakes.

Yes, I've always seen it as a hidden message embedded in your words, so you comment on the weather but you're actually saying that the elf has a concealed weapon.

That being said, you can just say your character is using thieve's cant. Unless you're livestreaming your games for money you do not need to perform everything your character does.

This is my favourite example of Thieves' Cant:

Thieves Cant is more than just verbal. It can also consist of hand signals and body language, or the use of props. Two thieves could have a perfectly normal conversation over a cup of tea, with no code or incriminating language being spoken:

• Two teabags (Bank robbery)
• The angle of the teacup handle (3 o'clock tomorrow)
• How many sugars they used (There's 3 in our crew)
• What hand they stirred with (It's an inside job; guards shouldn't be any trouble)
• The direction of the stir (Bring a murder piece, in case I'm wrong)
• How many rotations (your cut is 3x5 = 15k)
• Clinking the spoon after stirring (Alright... I'm in)
• Placement of the spoon (meet me behind the pub at sunset to work out the details)

They then both get up and walk away, without even having a sip.

You can look into all manner of means of getting across secret messages, from glyphs to slang. That's the mechanics behind it though; the implementation is between the user and your DM.

Were I your DM, I'd allow you to say "I use thieves' cant to communicate [my message]," and then proceed to have the conversation as normal except nobody else understand the actual message. But if you wanted to say "The idiot hamster has reversed into the sports lorry," and then follow up with your message, that'd be fine too. Depending on how comfortable you and your DM are goofing around, consider it an excuse to be as silly as you like. Once upon a time there were alignment languages, imagine how crazy that got!

I like Dael Kingsmill's take on it: 

+1 to Dael Kingsmill.  

Another take would be British Crime movies:

If you'd like to read actual published D&D references of Thieves' Cant, the AD&D 2nd Edition Complete Thief's Handbook had a small glossary of thief slang;

Quote from Plaguescarred >>

If you'd like to read actual published D&D references of Thieves' Cant, the AD&D 2nd Edition Complete Thief's Handbook had a small glossary of thief slang;

Box-Man: Strictly speaking, a thief specialized in cracking safes.
Burn: To underreport the take in a job to one's partners. "Luigi burned us. He told us there were only three diamonds, and kept two for himself."
Cannon: Pickpocket, cutpurse.
Contraband: Illegal goods (stolen or prohibited by local law).
Fencing: Selling stolen goods. "We stole the duke's jewels and fenced them later the same night."
The Fix: Ties with corrupt officials to have criminal charges "fixed"—that is, thrown out. This will usually require bribes or favors.
General Subscription: Money collected from the local underworld to free a captured thief by bribing officials.
Hit Man: Assassin; an "executioner" for crime bosses, paid to kill their enemies.
Lone Wolf: A solitary, independent thief. He is probably self-taught and not allied with a guild.
Made-Guy: A burglar who is in good standing with the local thieves' guild; a guildsman.
Mark: The target of a confidence game. "We have to bring the mark to the Burnt Goose Tavern."
Mob: A group of thieves.
Pennyweighter: A thief who operates by replacing valuable items (especially jewelry) with worthless ones.
Piece Man: Someone who trades knowledge on where stolen property can be sold.
Pigeon: Victim of a con or swindle.
Pigeon Plucker: Swindler, con artist.
Racket: Any sort of larceny, from pickpocketing and burglary through embezzlement.
Rootin': Committing crimes.
Roper: Someone who pulls in a mark for a con.
Rounder: A good, professional burglar.
Score: Loot from a theft. "We got a good score from the duke."
Squeal: To identify one's partners to the local authorities, usually in return for a lighter penalty for one's own crimes.
Tipster: Someone who has knowledge to share with burglars about good targets.

I remember that list!  And remember seeing it how as an odd mix of largely Victorian english (probably via Dickens) and 20th century english "crime" slang not tied to the same period.

To port dis round the rero to the Opie (see what I did there?), thieves cant isn't exactly fixed, or doesn't have to be.  Thieves cant is part a slang, and slangs evolve and transform faster than "official" language.  With a cant some of that is just the natural fluidity of slangs largely accelerated by the liminal, fragile, fugitive nature of a lot of criminal society.  Cant is also a code, and if the coppers are getting wise to the cant, overt efforts to change up the code are made.

So cant is partly a code but also a shibboleth ("talk the talk" is important in criminal syndicates before they trust you to "walk the walk" with them).

And if you want give your rogue a particular privileged roll as communicator with those elements, you could have moments where other characters make an effort that plays out like this:

Thief's cant was based on the rhyming slang used by british underclass in 19th century cockney slums.

I am Hank Marvin so I turned Tea Leaf and Half-Inched some Tom Foolery.  Where can I get some Beans and Honey for the Tom?

I am starving, so turned Thief and pinched some Jewelry.  Where can I get some money for the Jewelry.

Quote from MidnightPlat >>

Quote from Plaguescarred >>

If you'd like to read actual published D&D references of Thieves' Cant, the AD&D 2nd Edition Complete Thief's Handbook had a small glossary of thief slang;

Box-Man: Strictly speaking, a thief specialized in cracking safes.
Burn: To underreport the take in a job to one's partners. "Luigi burned us. He told us there were only three diamonds, and kept two for himself."
Cannon: Pickpocket, cutpurse.
Contraband: Illegal goods (stolen or prohibited by local law).
Fencing: Selling stolen goods. "We stole the duke's jewels and fenced them later the same night."
The Fix: Ties with corrupt officials to have criminal charges "fixed"—that is, thrown out. This will usually require bribes or favors.
General Subscription: Money collected from the local underworld to free a captured thief by bribing officials.
Hit Man: Assassin; an "executioner" for crime bosses, paid to kill their enemies.
Lone Wolf: A solitary, independent thief. He is probably self-taught and not allied with a guild.
Made-Guy: A burglar who is in good standing with the local thieves' guild; a guildsman.
Mark: The target of a confidence game. "We have to bring the mark to the Burnt Goose Tavern."
Mob: A group of thieves.
Pennyweighter: A thief who operates by replacing valuable items (especially jewelry) with worthless ones.
Piece Man: Someone who trades knowledge on where stolen property can be sold.
Pigeon: Victim of a con or swindle.
Pigeon Plucker: Swindler, con artist.
Racket: Any sort of larceny, from pickpocketing and burglary through embezzlement.
Rootin': Committing crimes.
Roper: Someone who pulls in a mark for a con.
Rounder: A good, professional burglar.
Score: Loot from a theft. "We got a good score from the duke."
Squeal: To identify one's partners to the local authorities, usually in return for a lighter penalty for one's own crimes.
Tipster: Someone who has knowledge to share with burglars about good targets.

 

I remember that list!  And remember seeing it how as an odd mix of largely Victorian english (probably via Dickens) and 20th century english "crime" slang not tied to the same period.

To port dis round the rero to the Opie (see what I did there?), thieves cant isn't exactly fixed, or doesn't have to be.  Thieves cant is part a slang, and slangs evolve and transform faster than "official" language.  With a cant some of that is just the natural fluidity of slangs largely accelerated by the liminal, fragile, fugitive nature of a lot of criminal society.  Cant is also a code, and if the coppers are getting wise to the cant, overt efforts to change up the code are made.

So cant is partly a code but also a shibboleth ("talk the talk" is important in criminal syndicates before they trust you to "walk the walk" with them).

And if you want give your rogue a particular privileged roll as communicator with those elements, you could have moments where other characters make an effort that plays out like this:

 

I watch this scene every time I see it posted. This too, is how I like to imagine Thieves' Cant.

This might also be a helpful video

As a new DM, I had a new instances the NPC engage with the PC in thief cant.

1. An illegal organization that give sketchy quest via drink order (think Deadpool movie). Are you ordering a Bloody Mary, or Richie Cocktail? Are you accenting the drink with little green? or dragon red? the PC was a little confused, but one of them managed to get the hint and somehow it works.

2. Sign language. Inspired by the Maiden of the Spear's Handtalk from Wheel of time.

3. And when all else fails : "I say in Thief Cant 'blah blah blah..' "

I always interpreted it as a language hidden in plain sight within another commonly-understood language as I find that more interesting, but...

There is a stream I watch where only one of the players understood what Thieves' Cant is, but the others (DM included) thought it was like any other foreign language instead. When the player used Thieves' Cant for his character—merely stated as using Thieves' Cant—and the others decided they understood the name of a place as spoken between the two characters, he was unable to convince them than the place name was encrypted and they shouldn't be able to understand it. They all (DM included) kept insisting it was just another language and the place name, being a Common name, would be understood in any language as the place name would be spoken in plain Common regardless.🤦🏻‍♂️

The comments on that stream were peppered with people trying to explain how Thieves' Cant worked.

Then again, all the players (including the Rogue and DM) in that stream interpreted Thunder damage to be Thor damage (as in Lightning damage), and the Thunderwave spell is canon as Lightning damage in their setting even after they realized what the difference is. So, it is also canon in their setting that Thieves' Cant is just another foreign language only a select few understand, but common names are still spoken in plain Common.🤦🏻‍♂️

They're all slowly learning the rules, though. This year, they just added the mechanics of Spell Slots (versus "Spells? Lots!" as the Bard said). They still kept electric Thunderwave, though. Eldritch Blast is also Lightning Damage in their setting even though it's officially Force damage. It's like the only damage types are Poison, Piercing, and Lightning for them. (They also make up damage types such as Embarrassment or Faceplant damage.)

It's rather funny how loose (and seemingly unaware) they are with the core D&D rules, which is why I like to watch them. Easy mode D&D. I watch plenty of Normal and Hard mode D&D streams already.

EDIT: Funnier still is how they have different Thieves' Cant dialects and accents, which I can actually imagine in a weird way. For example: A brutish pirate using a rather formal version of Theives' Cant and sounds extremely learned only when speaking Thieves' Cant with the party's Rogue but like an uneducated lout when speaking Common to everyone else.

Quote from Mog_Dracov >>

Thief's cant was based on the rhyming slang used by british underclass in 19th century cockney slums.

 

I am Hank Marvin so I turned Tea Leaf and Half-Inched some Tom Foolery.  Where can I get some Beans and Honey for the Tom?

I am starving, so turned Thief and pinched some Jewelry.  Where can I get some money for the Jewelry. 

 I wasn't sure if it was intended to be pretty much the exact same thing, but I have always equated thieves' cant with Cockney rhyming slang.

Cockney rhyming slang is a good reference for what a Thieves Cant could be, and can be fun for those who want to put in the work, but Cockney Rhyming slang isn't the limit of Thieves Cant.  "Rhyming" doesn't work well in a lot of languages that haven't been through English's contortions the past 1000 years.  Call it a demimonde, underworld or whatever, but every society has a a society on its edges or backrooms where a language is spoken that seems foreign to folks not exposed to that world,