five-mcp

MCP server for the FIVE Persona Engine — an LLM persona constraint engine that generates structured JSON constraints to eliminate persona drift. Instead of describing personality in words (which LLMs interpret differently each turn), FIVE defines behavioral parameters the LLM executes as a recipe. See how it works →

Measured: with the constraint JSON + free harness, the demo character survived a 120-turn pressure test with zero persona breaks (plain prompt: 8 breaks; JSON alone: 1). Numbers, transcripts and scripts →

Free — no API key, no account.

Quick Start

Install

pip install five-mcp

Use with Claude Desktop

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "five-character-engine": {
      "command": "five-mcp"
    }
  }
}

That's it — no environment variables needed.

Use with other MCP clients

Any MCP-compatible client can connect via stdio transport:

five-mcp

Tool: generate

Generates persona constraints via the FIVE engine.

Parameters

Response

{
  "status": "ok",
  "constraint": { "..." }
}

Rate limits

The API is free. To keep it available to everyone, a light per-IP limit applies: 10 requests/min, 200 requests/day. The free host may cold-start, so the first call can take up to a minute.

Links

• API & Docs: fiveengine.dev
• GitHub: github.com/kiro0x/five-mcp
• Design philosophy & examples: five-character-engine README
• Measured evaluation (120-turn drift test): five-character-engine eval/
• Engine repo: github.com/kiro0x/five-character-engine

License

MIT