We Built a Mythology Engine as an MCP Server

What if your AI could generate characters that fit your world — its specific history, factions, magic system, and political tensions — instead of producing generic heroes that could belong to any setting? We built that. It is called the Arcanea MCP server, and it ships as a single npx command.

What is MCP?

The Model Context Protocol is a standard for giving AI assistants structured access to external tools. Think of it as USB for AI: the protocol defines how tools connect, and any compliant host — Claude, Cursor, Windsurf, Zed — can use them without custom integration code. You define a server with typed tools and schemas. The AI calls them like functions. The results feed back into context.

What makes MCP interesting for creative systems is that it turns an AI assistant into a stateful collaborator. The AI is not just generating text against a blank context — it is calling into a system that knows your world, remembers what you created yesterday, and can check new content against rules you established six months ago.

What We Built: 34 Tools Across 6 Categories

The Arcanea MCP server is a mythology engine. It does not generate content in a vacuum — it generates content that is coherent with a specific world that you define and that grows richer with every session.

The Creation Graph

Most worldbuilding tools generate content in isolation. You get a character, a location, a magic system — but they exist as separate files with no relationship to each other. The Creation Graph changes this. Every element you create can be linked to every other element. A character can be linked to the faction they lead, the artifact they carry, the location where they were born, and the prophecy they are destined to fulfill. Call get_world_graph and you receive a traversable map of your entire world — not a list of documents, but a living network of relationships.

suggest_connections takes an element and surfaces latent links that you may not have noticed: a creature whose habitat overlaps with a villain's stronghold, a character whose backstory creates a conflict with an existing faction. The AI finds the structural tensions you built without realizing it.

Memory Vaults: Your World Persists

Six semantic vaults store your world across sessions: characters, locations, artifacts, factions, lore, and events. Each vault supports semantic search — not just keyword lookup but meaning-based retrieval. Ask for "a character with a tragic backstory tied to the Fire Gate" and the vault returns the closest match from everything you have built, ranked by semantic distance. Your world does not reset when the conversation ends. The AI walks back into your world with full context on every new session.

The Feature That Changes How You Build

world_report is the tool we are most proud of. It analyzes the structural health of your world — coverage across factions, character archetypes, narrative roles, conflict vectors — and tells you what to create next. Not "add more content." Specific gaps with specific consequences.

"You have 5 warriors but no healer — your party will die in Act 3. Your northern faction has no known enemies, which means they have no narrative function. Your magic system lacks a cost, which means it lacks drama."

This is the difference between a generative tool and an intelligence. A generative tool produces content on demand. An intelligence looks at what you have built and tells you what is missing, what is structurally weak, and what you should build next to maximize coherence and narrative tension. generate_conflict and weave_narrative then help you fill those gaps with content that fits.

Install in 3 Lines

The server supports HTTP and SSE dual-transport. Add it to your AI tool of choice:

{
  "mcpServers": {
    "arcanea": {
      "command": "npx",
      "args": ["-y", "@arcanea/mcp-server@latest"]
    }
  }
}

{
  "mcpServers": {
    "arcanea": {
      "command": "npx",
      "args": ["-y", "@arcanea/mcp-server@latest"]
    }
  }
}

npx @arcanea/mcp-server@latest --port 3001 --transport http

Under the Hood

The server is built on the MCP SDK 1.29 using the tool() API introduced in the current SDK generation — no legacy switch statements, no 47-case dispatch. Each tool is declared with a Zod schema for input validation, which means malformed tool calls fail fast with clear error messages rather than silently producing garbage. The dual-transport layer supports both HTTP for persistent servers and SSE for streaming contexts, so the same server binary works in Claude Desktop, Cursor, and any HTTP client.

Tool calls are stateless at the protocol level but stateful through the vault system. The server holds no in-memory world state between calls — every call reads from and writes to the vault layer, which means the server can restart without losing your world and multiple clients can connect to the same vault simultaneously without conflicts.

What Comes Next

The server is open source. The repository will be published to the Arcanea OSS organization within the next sprint, and the npm package will be available under @arcanea/mcp-server. Marketplace listings for the Claude and Cursor extension stores are in progress.

The longer arc: your world, your rules. The vault system is designed to be self-hostable with your own storage backend. You can define custom canon rules that the validation tools enforce. You can extend the tool set with domain-specific generators for your specific genre — military science fiction, secondary world fantasy, cosmic horror. The mythology engine is the substrate. What you build on it is yours.

The best worldbuilding tool is the one that knows your world. Every call makes it smarter. Every session adds to what it knows. Your world compounds.