Mythic GME MCP Server

A Mythic Game Master Emulator 2nd Edition implementation as an MCP server. Perfect for solo RPGs or GM-less sessions.

Tools

Tool	Description
`check_scene`	Start a scene - Normal, Altered, or Interrupted?
`roll_fate`	Ask a yes/no question with given odds
`get_chaos`	Get current Chaos Factor (1-9)
`set_chaos`	Set Chaos Factor to specific value
`adjust_chaos`	Increment or decrement Chaos Factor
`characters`	Manage NPCs list (add/remove/list/roll)
`threads`	Manage plot threads (add/remove/list/roll)

How It Works

Scene Check

When starting a new scene, roll d10 vs Chaos Factor:

Result	When	Meaning
Normal	Roll > Chaos	Scene proceeds as expected
Altered	Roll ≤ Chaos, even	Same scene with a twist
Interrupted	Roll ≤ Chaos, odd	Completely different scene

The Fate Chart

Ask the oracle a yes/no question with odds from impossible to has_to_be.

Results: Yes, No, Exceptional Yes, Exceptional No, or Random Event (on doubles).

Chaos Factor

Represents how out of control the story is (1-9). After each scene:

Scene went as expected → decrease chaos
Scene spiraled out of control → increase chaos

Characters & Threads Lists

Manage NPCs and plot threads using the Mythic 2e chunking system:

Structure:

25 slots organized into 5 groups of 5
Items can appear up to 3 times (for weighting)

Actions:

add - Add item to next empty slot (same item up to 3x)
remove - Remove all occurrences of an item
list - View the current list
roll - Random selection using weighted chunking

The Chunking Mechanic:

Roll to select a group (die size based on item count)
Roll d10 to select slot within group (1-2=S1, 3-4=S2, etc.)
If slot is empty → CHOOSE any item that fits, or reroll

Adding important items multiple times increases their probability of being rolled!

Usage

With OpenAI Responses API

const response = await openai.responses.create({
  model: "gpt-4o",
  input: "Add 'The Dark Lord' to the characters list, then start a new scene",
  tools: [{
    type: "mcp",
    server_label: "mythic",
    server_url: "YOUR_ENDPOINT_URL",
    require_approval: "never",
  }],
});

Direct Testing

# Add a character
curl -X POST YOUR_ENDPOINT_URL \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"characters","arguments":{"action":"add","name":"Gandalf"}}}'

# Roll on characters
curl -X POST YOUR_ENDPOINT_URL \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"characters","arguments":{"action":"roll"}}}'

# List threads
curl -X POST YOUR_ENDPOINT_URL \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"threads","arguments":{"action":"list"}}}'

Example Session

You: Add Frodo, Sam, and Gandalf to the characters list. 
     Add "Destroy the Ring" as a thread (twice since it's important).

AI: [adds characters and threads]
    ✅ Added "Frodo" to slot 1
    ✅ Added "Sam" to slot 2
    ✅ Added "Gandalf" to slot 3
    ✅ Added "Destroy the Ring" to slot 1
    ✅ Added "Destroy the Ring" to slot 2

You: Start a new scene - we're entering Moria.

AI: [checks scene] 🔄 Scene Altered - Roll: 4 vs Chaos 5
    The scene happens, but something's different...

You: Roll a random character to see who causes trouble.

AI: [rolls characters] 🎲 Gandalf
    Group roll: 2 → Group 1
    Slot roll: 5 → Slot 3

You: Is there a Balrog here? (very_unlikely)

AI: [rolls fate] 🎲 Exceptional Yes - Roll: 3 vs threshold 20
    Not just a Balrog... something worse!

dcm31

mcp-mythic