An Open-Source Agentic Gaming Studio
Fourth Wall Gaming
AI gamemasters, worlds, art, and stories — built on the Mythras and Classic Fantasy ORC rules.
A table where the gamesmaster never forgets a wound, a debt, or a name. You speak; the world answers. The dice are honest, and the ledger is kept.
How a check resolves at this table
| d100 | Roll under your skill. The difficulty grade — Easy to Herculean — is declared before the dice fall. |
| ⚔ | Combat runs the full Mythras exchange: differential rolls, special effects, hit locations, armour, wounds. |
| ✦ | Every roll is returned as auditable JSON. The gamesmaster cannot fudge. |
Play It Now
Install the Mythras GM plugin for Claude Code, pick a campaign — Purewater or the Veilwrack — and open the first scene. Your campaign lives in a knowledge graph: walk away mid-scene, return weeks later, and the GM recaps exactly where you stood.
Run your first session →Creating Veilwrack
AI-assisted doesn't mean derivative. How the Veilwrack was made: its antecedents named honestly, its original ideas defended, and what worldbuilding at machine scale actually looks like.
Why this isn't slop →Behind the Screen
A deterministic d100 rules engine, a TypeDB knowledge graph as the save file, and campaigns published as Git repos. Serious engineering in service of the game.
How it works →The Talk · LLM-Day San Francisco · 1 October 2026
Claude Opus as a Tabletop Roleplaying Gamesmaster
What it takes to run Mythras Imperative inside a language model, and why a model on its own will not do it: a universal rules engine that rolls honestly, a living world of NPC agendas on clocks that turn whether or not you are watching, and an epistemics layer where what each character knows is a projection from one shared source of truth.
The slides are live — arrow keys move through them, and one of them replays a real scene of play as it was typed at the table.
The Catalogue
Mythras GM
A Claude-powered Gamesmaster for Mythras Imperative. Rules engine, combat resolution, character generation, campaign publishing — all persisted in TypeDB.
The engine, on GitHub →The Veilwrack: The Stilling
An original sky realm. No ground — winged peoples on the calcified husks of dead sky-leviathans, and the wind itself is dying. 46 lore entries, 7 factions, a five-act arc.
The worldbook, on GitHub →Gallery
Art, and eventually film and comics, generated alongside the worlds — every piece traceable to the campaign canon it illustrates.
Browse the gallery →Built on Mythras — Get the Real Game
Everything here runs on the Mythras Imperative SRD under the ORC License. Mythras is one of the finest d100 systems ever written: fast, deadly, deeply simulationist. If you enjoy playing it with an AI gamemaster, buy the books and play it with your friends.
The Design Mechanism publishes Mythras, Mythras Imperative, and Classic Fantasy.