A downloadable system

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Ever wondered how to make your own TTRPG? Welcome to v1.0 of Caltrop Core, an introductory game design system using the humble and sharp d4! Developed with @aghostofeli and @n_quests on Twitter, it's extremely simple and bare bones so anyone can make a game with it, regardless of your experience level! It can have as much or as little complexity as you like.

I'm new to game design as well, but often the hardest thing about trying something new is getting started. So I wanted to provide a deeper explanation of how to use the dice core for anyone that's new to this!

There's a suggested donation of $1, but please download for free (especially if you've already made a game with CC!). You can always come back later and drop a few dollars if you found it worthwhile. The screenshots on this page has everything you need to use the system, so really, go for it! All I ask is you let me know what you make with it! Add "Built on Caltrop Core" or "A Caltrop Core TTRPG" to your doc, as well as the attribution text, and you're good to go! Additionally, a link to my Twitter (https://twitter.com/titanomachyRPG) and/or my Itch (https://titanomachyRPG.itch.io) would be greatly appreciated.


This work is based on Caltrop Core, published by Titanomachy RPG. The Caltrop Core SRD is licensed for use under a Creative Commons Attribution 4.0 International License..

Creative Commons License

CategoryPhysical game
Rated 4.9 out of 5 stars
(110 total ratings)
GenreRole Playing
Tagsd4, dice-core, Game Design, Indie, poc-made, srd, Tabletop role-playing game


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Click download now to get access to the following files:

Caltrop Core v1.0.pdf 445 kB
Caltrop Core Classic (v0.0).pdf 501 kB
Caltrop Core Classic 1 page.pdf 471 kB
Built On Caltrop Core (Transparent).png 22 kB

Development log


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Is there going to be a Caltrop Core Jam #3?

Awesome system that I am excited to use!

Yay thank you!! I'm so glad!

Thanks for creating Caltrop Core! I've played a couple of games that run with it, and the sole fact that people can bring their games to life thanks to this SRD is marvelous!


I wrote a one-page game with this. Really fun and intuitive! (Caltrop Core, not my game, though don't consider it unlikely I'll compliment my own work :p )


On October 5th, 2021, Lex Kim Bobrow, or TitanomachyRPG on Twitter, released the first iteration of what is now known as the Caltrop Core SRD. Named by Dicebreaker as one of the “best tabletop RPG systems to hack into a custom game,” the Caltrop Core is the foundation for over one hundred TTRPGs.

I love the concept, but personally don't care for how the statistics work out for rules-as-written. I would make the following modifications at my table:

  1. Disadvantage: if the character is hindered by injury or circumstances, role 2d4 and take the lowest.
  2. There are three possible outcomes: 4 = Success, 3 = Mixed Success, 2 or 1 = Failure. (You could grant "critical success" for rolling more than one 4).

The consequences of these changes are shown here: https://anydice.com/program/27ee5

I just released a new Caltrop Core game! It helped me a lot in making sure I got my game released within a day, which I forced myself to do so I could release it on creator day. 

I'm so glad!!

Built a game. Here: https://jackledead.itch.io/bio-fear-rpg


Caltrop Core is a d4 tabletop roleplaying game engine.

The PDF 11 pages, with a bold and easy to read layout, and the mechanics are simple to learn and use.

Essentially, the way CalCore works is you roll a pool of d4s and count the highest. 3 is a partial success and 2 a partial failure, so as long as you're rolling multiple dice you have odds of making progress.

The engine explicitly supports both stat-driven and token-driven gameplay (think DnD vs Belonging Outside Belonging,) and it comes with a robust sample game built with the engine, so just by reading it you can get a glimpse of the engine's capabilities and range.

The sample game is fully playable, as are the tons of other neat titles that have been written using Caltrop Core.

Overall, if you want to try some low-number-dice tabletop design, Caltrop Core is a neat little engine and absolutely worth a look.


Already started making a game with this system, and made an itch account just to write this and put my game out there. So cool


Aww!! Thank you so much, I hope it serves you well!!

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That's delightful! The first game I ever made was for Caltrop Core, and so it's the first thing I published :) Looking forward to seeing what you do!


I really like this but I was thinking my players would hate it (they are mostly only familiar with DnD 5e).  The d4s would be a big sticking point... then I realized I was an idiot... just use d20s and take the highest. Same tables but times 5: 1-5 Absolute Failure, 6-10 Partial Failure, 11-15 Partial Success, 16-20 Absolute Success. 

I know this kind of defeats the "Love for the unloved d4s" but I think I would have an easier time selling it...


Go for it! I also found d12s that are done up to be d4s (so similar idea as yours), and they feel nicer to roll!


A dead simple system that somehow strikes the perfect balance between being perfectly approachable and incredibly firm a foundation to build numerous (very different) games upon.


Thank you so much for the kind words. I'm so honored by everyone's response. And the fact that so many WILDLY different games have been COMPLETED using it means I can't dodge the compliments the way I normally would try to haha. Truly so glad you like it.

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Hmmm… I notice that there doesn't appear to be any way to reflect situational modifiers.

Suggestion: Add or subtract D4s from the basic dice pool.

Say a character is trying to scale a wall. If it's just a standard brick wall, the roll for that might be a pool of (Dexterity) D4s.

But what if it's raining? That would make it harder to climb, so subtract one from the pool—that is, roll (Dexterity - 1) D4s. And if it's really raining, I mean a torrential downpour, the character might need to roll (Dexterity - 2) D4s, or perhaps even worse.

If the wall has a bunch of bricks sticking out which are usable as handholds and footholds, that would make it easier to climb, so go with a pool of (Dexterity + 1) D4s.

And so on, and so forth.

If you choose to make use of this suggestion, you should prolly decide what to do if the pool penalties reduce the pool to zero dice or less. Perhaps the simplest way to go might be to declare the minimum dice pool to be 1D4, end of discussion. There are other alternatives, which are somewhat more complex.


Those are fantastic ideas! I may add a little section in a future version about ways to handle situational modifiers. I want it to be up to each designer, but having examples doesn't hurt whatsoever. Thanks for the idea!


if zero dice then either you can't do it or roll 2 (or more) dice and take the lowest. my 2 cents :D


(nods) Yep; "roll N dice, take the worst" was one of the "somewhat more complex" alternatives I waved my hands in the general direction of.

I like how simple the system is but I have a critique:

I don't like how there's no probability behind certain proposed mechanics, such as the possibility of using the sum of d4s for a mechanic, or how often a player might get a 4 on using X amount of d4s. 

The core of it's great. Really like the whole "First design" aspect.


You're so right! And I don't really have an excuse, a bunch of people sent me awesome probability tables, like this one by @aaronsxl on Twitter. I'll have to add it to the SRD in the next update! I do have enough info now for a v0.1 for sure. Thanks for checking out Caltrop Core!

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And inverted these same numbers would apply to a "roll Xd4 and take the lowest"!

That's the mod I would make - good things effecting a roll add dice (up to a max of 4) while bad things "remove" dice (down to a max of 4).  Below 1d4 is -2d4 and so on; the minus means take the lowest.  I would also make 4 the max instead of 5 since they're so similar, and because 4 is a 4 and we're all about 4s.  so:


This allows for games with truly miserable results happening under certain situations which can be ~FUN~ :)

P.S. I love the d4 and have also done some experimenting with it


This is awesome! Super cool idea!!

I love how the tiered success gets even more nuanced than I usually see results in TTRPGs get, with the Full Failure, Partial Failure, Partial Success, Full Success results. I'm also a fan of the different ways to put together dice pools. Thinking of putting something together for friends with it.

That's awesome! I'm so glad! And I'm sure there are even more cool ways to group the d4s and get results. If you find anything cool as you make stuff for friends, let me know!!


This is great! I'm really excited to start making games with this system (and use them for the power of GOOD).

Hey, thanks for making this! Used it for a one-shot for my podcast and it was a wonderfully approachable system that really helped us tell the kind of story we were trying to tell. I adore the simplicity and flexibility of it. 

Keep up the great work!

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Just finished reading through this and have to say, this is a brilliant core. I can't wait to use it. It's made with such a beautiful and clear design purpose.

All the best!

Thank you so much!! That means a lot! I can't wait to see what you make!!


This looks so simple and approachable~! Keen to try and make/play a game with this system asap!

Thanks!! I hope you enjoy the process, and I can't wait to see what you make!

Just finished making my game! I'll link on twitter (I'm StuartH_VA there)

Heck yes!!


I actually just started working on a little game using this! Should be done in the next few days.

Love to hear it! Tag me on Twitter so I can see (if you post)!

Will do!


I actually adore this system. I’m super-new to making TTRPGs but I have so many ideas that would work with it - I’m going to make something awesome utilising it


I'm so happy to hear that!! I'm also new, and I thought this would be a great tool for people like us!


This is such a beautifully simple system. I'm going to make my first game with this.

Thank you so much! Please let me know when you do! I'd love to see it!