Karsus Codex turns "wouldn't it be cool if..." into a Baldur's Gate 3 mod you can actually install. No modding experience, no toolchain, no problem. We built a web app to do all the technical work so you wouldn't have to. Honestly, mostly so we wouldn't have to.
Forge Bot builds only weapons, for now. If you are dreaming of rings, cloaks, armor, or boots, there is a wizard for that too.
You bring the concept, we bring the code.
Larian's official toolkit is a real modding tool, built for professionals, by professionals. That means, like most tools for professionals, it can be hard to navigate for the beginner. While I admire the people who use it with ease, it just wasn't for me. But I still want to make cool stuff!
I figured other people might feel the same, and thus Karsus Codex was born... a wizard for making items. But then I realized it could be even easier, and added Forge Bot, a way to build via chat.
Describe the weapon to whatever AI you already use. It writes the recipe, you paste it back here. Fast, no forms, and you never see a dropdown. The prompt provided keeps the JSON formatted correctly, and if it's not, we'll just tell you.
Weapons, for now.
Screens, lists, a final summary page before you save the item. No JSON anywhere, and it reaches the parts of the game the recipe format hasn't grown into yet.
Weapons, armor, rings, cloaks, boots, and so on.
There's a prompt sitting on the Forge Bot page. Copy it, paste it into Claude, ChatGPT, pick your poison. It tells your AI to go read the capability document (the machine-readable list of every weapon type, effect, and passive we can actually build), and then interview you about the weapon you want - one question at a time. If your AI can't browse the web, the same page has the document sitting right there to paste instead. That document is what stops your AI confidently inventing a damage type that has never existed (+1d4 emotional pain isn't a thing; looking at you, Claude).
/api/recipe/capabilities weapon_types 33 · dagger, rapier, greatsword, ...Describe it in concrete terms - a +1 greatsword with frost damage - or skip the stats and just explain what you want. Your AI writes the recipe; in the meantime, karsuscodex.com sits idly by, awaiting your triumphant return. That is to say, we outsourced this step to you, which is either reassuring or suspicious depending on your temperament.
"a rapier that drinks a little health when I crit. tragic disgraced-noble energy. rare, but not so strong it's embarrassing"
Drop the JSON on the site. If something's wrong we hand back a plain-English error written so you can paste it straight back into the same chat. It'll fix it and you paste again. That loop is the whole thing, really. Once we have valid JSON, it submits and you land on the wizard's review step, so you get one last look - and a chance to fiddle - before you hit build. You can keep editing it to your heart's content in the wizard, or just throw it out and start again. And not even feel bad about it, because it's simple.
When it's valid, you're just a click or two away from downloading it - or you can add it to a mod with other items you made, or from the shared library. Either way, you get a .pak file, ready for your BG3 Mods folder.
On Windows and Mac, the .pak goes in your Baldur's Gate 3 Mods folder, and the in-game Mod Manager takes it from there. Console? Sorry. Truly. We'd help you out if we could - once we get Mod.io integration, maybe?
Documentation coming soon: how to push your creation up to Nexus Mods and mod.io, so other people can play with it too.
OK, so I pasted the JSON and hit the button...
Whether you talked to your AI or clicked your way here, this is the last screen before a mod exists. A valid recipe opens right here, already filled in, so you can see what your AI actually committed you to, and change your mind about any of it.
Check out the wizard - login requiredThat's the real reason accounts exist. Your items live in your library, where you can come back to tweak them, rebuild them, or bundle them into mods. Everything starts private; mark an item public and it joins the shared library for other people to play with.
Armor, spells, and consumables are the obvious next things. They are not here today. Saying otherwise would just waste your evening.
If you generate a dagger that does 4d12 psychic damage, gives you crit immunity, and 30 AC, that's not our fault, and we hope you enjoy.
Patches can break things. Ours, or Larian's.
Neither Forge Bot nor the wizard currently supports uploading your own art, or generating any. Listen, even Karsus has limits, and we're actually not Karsus anyway.
The website exists because I understand the web better than I understand the BG3 Mod Maker tool; Simply put, I got frustrated trying to use the actual toolkit, and figured it would be way easier to use a website like this one, if only it existed. So I spent hundreds of hours to build something to save me dozens of hours. Classic engineering move. You're welcome.
TLDR - Make items, easily, for free, from idea to download in a couple minutes. The hardest part is gonna be finding your Mods folder, but we believe in you. Worst case scenario: you end up with a rapier you don't like. We think that's a pretty good deal.