MythxEngine
io.github.protoLabsAIPublished by GitHub account protoLabsAIv0.3.0Updated Oct 24, 2026
Tabletop RPG engine over MCP: dice, combat, stress, clocks, world generation, four bundled worlds
Overview
A tabletop RPG engine that lets an AI act as game master, with deterministic dice, combat, stress, clocks, world generation and four bundled worlds.
- What you can do
- Run sessions and characters: create sessions, load world summaries, create characters with HP, stress and gear
- Resolve tests and consequences: roll tests with position and effect, push rolls, resist consequences, look up rules
- Track combat: start combat, roll initiative, attack, with armor, conditions and damage
- Manage clocks and world state: tick situation clocks, track investigations and NPC relationships, generate worlds
- Look up and generate rulebook content from the same source the engine uses
- When to use it
- Useful when you want an assistant to run or assist a tabletop role-playing game with consistent, seeded mechanics rather than improvised rulings, or to explore the four bundled starter worlds.
- Requirements
- Runs locally over stdio as an npm package (Node 22.13 or newer) or as a Claude Desktop extension bundle that ships its own Node runtime. Optional RPG_MCP_DATA_DIR sets where sessions and world packs are stored; no authentication is declared.
Installation
In SourceWeft
- Open MythxEngine in the dashboard and add it to a workspace.
- Enable the server for the chats that should use its tools.
Desktop only via STDIO. STDIO servers start a local process, so they need the SourceWeft desktop host.
Other MCP clients
Follow the launch instructions in the repository.
README
MythxEngine — tabletop RPG engine over MCP
[CI] [npm] [license: MIT] [node]
A complete tabletop RPG engine your AI can run: deterministic dice, five-tier outcomes, FitD-style stress, combat tracking, situation clocks, investigations, NPC relationships, world generation — 134 tools over the Model Context Protocol, with four complete starter worlds bundled in.
Claude (or any MCP client) becomes your Game Master. The engine keeps the rules honest: same seed + same actions = same outcome.
Install
Claude Code — plugin (skills + tools, recommended)
One install delivers the MCP server plus play skills (/rpg:play,
/rpg:combat-mode, /rpg:world-building-mode, …).
Claude Code — tools only
Requires Node >= 22.13.
Claude Desktop
Download mythxengine-<version>.mcpb from the
latest release and
drag it into Settings → Extensions. No other setup — Claude Desktop ships
its own Node runtime.
Five-minute walkthrough
Everything below is one conversation with Claude after installing. Four worlds are imported on first run — Port Miriam (harbor noir), Aethelgard (mythic frontier), Threshold Deep (weird depths), and the Treehouse Anthology.
1. Pick a world, make a character.
Start a session in Port Miriam. I want to play a dockside fixer who owes the wrong people money.
The GM calls create_session, load_world_summary, and create_character —
your fixer gets HP, stress, gear, and a spot in the world's faction web.
2. Roll with real stakes. Every test is framed with position (how bad is failure?) and effect (how much does success buy?):
I try to slip past the harbor patrol to reach the smuggler's skiff.
Five outcomes — critical success, success, partial, failure, critical
failure — and on a bad roll you can push_roll (spend 2 stress for +1d6) or
resist_consequence to buy the severity down. Stress is a real currency;
overflow means trauma.
3. Fight a combat round.
Two dockhands block the gangway. I draw my hook-knife.
start_combat → roll_initiative → attack — initiative order, armor,
conditions, and damage all tracked; every attack returns the same five-tier
outcome with suggested GM moves on a miss.
4. Watch a clock tick. The patrol you dodged? The GM started a
harbor-alert clock. Fail forward enough times (tick_clock fires
automatically on partials/failures when wired) and the dock lights come on —
consequences arrive on schedule, not by fiat.
That's the loop: fiction in, mechanics out, consequences on clocks.
What's in the box
Rules & docs
- docs/RULEBOOK.md — the complete rules, all 12
chapters (outcomes, position & effect, tests, stress, combat, conditions,
gear, time & clocks, GM moves). Generated from
packages/rulebook, the same source thelookup_ruleandgenerate_rulebooktools serve — so it never drifts from the engine. - docs/engine.md — how the engine works: the five-tier outcome system, position & effect, stress, deterministic RNG, and how the packages fit together.
- agent-kit/ — a portable GM system prompt and operating manual for running a game with any agent.
Want the full experience?
This repo is the engine. MythxEngine Desktop is the game: a visual frame-based play surface, scene imagery, generated world books, and polish. Follow along and get notified when it ships at mythxengine.com.
Development
See CONTRIBUTING.md — this repo is a downstream mirror of a private monorepo; issues are the fastest way to get fixes in.
License
MIT © protoLabs Studio
Source: README.md at commit 5c50567
Tools
0Version history
1- v0.3.0LatestSep 16, 2026
Score
50% of the applicable checks met
How complete this listing is, computed from the registry entry, the endpoint and public sources. Not a rating of the server and not a statement that it is safe or working today: reachability is a dated check, and no installs or reviews go into the score.
- Reached in the last 30 days25 pts
Keep the endpoint answering the MCP handshake; SourceWeft probes it every 30 days.
- Auth declared10 pts
Declare the credential headers in the registry entry, or keep the endpoint answering the probe so its auth can be classified.
- Tools listed15 pts
Answer tools/list without a credential, or ship a package that starts in a sandbox without one.
- DescriptionRequired15 pts
- Logo10 pts
- Documentation15 pts
- License10 pts