Polybrain MCP Server

An MCP (Model Context Protocol) server for connecting AI agents to multiple LLM models. Supports conversation history, model switching, and seamless Claude Code integration.

Features

• Multi-model support (OpenAI, OpenRouter, custom endpoints)

• Conversation history management

• Switch models mid-conversation

• Extended thinking/reasoning support (configurable by provider)

• Pure MCP protocol (silent by default)

• Automatic server management

Related MCP server: LLM Bridge MCP

Installation

npm install -g polybrain
# or
pnpm add -g polybrain

Quick Setup

1. Configure Models

Option A: YAML (recommended)

Create ~/.polybrain.yaml:

models:
  - id: "gpt-4o"
    modelName: "gpt-4o"
    baseUrl: "https://api.openai.com/v1"
    apiKey: "${OPENAI_API_KEY}"
    provider: "openai"

  - id: "gpt-5.1"
    modelName: "openai/gpt-5.1"
    baseUrl: "https://openrouter.io/api/v1"
    apiKey: "${OPENROUTER_KEY}"
    provider: "openrouter"

Set env vars:

export OPENAI_API_KEY="sk-..."
export OPENROUTER_KEY="sk-or-..."

Option B: Environment variables

export POLYBRAIN_BASE_URL="https://api.openai.com/v1"
export POLYBRAIN_API_KEY="sk-..."
export POLYBRAIN_MODEL_NAME="gpt-4o"

2. Coding Agent Integration

Claude Code

Run the following command to add Polybrain to Claude Code:

claude mcp add -s user -t stdio polybrain -- polybrain

OpenAI Codex

Open ~/.codex/config.toml and add:

[mcpServers.polybrain]
command = "polybrain"

Usage

You can now ask your coding agent to consult specific models. For example:

"Ask deepseek what's the best way to install python on mac"

Or:

"What models are available from polybrain?"

Configuration Reference

Environment Variables

• POLYBRAIN_BASE_URL - LLM API base URL

• POLYBRAIN_API_KEY - API key

• POLYBRAIN_MODEL_NAME - Model name

• POLYBRAIN_HTTP_PORT - Server port (default: 32701)

• POLYBRAIN_LOG_LEVEL - Log level (default: info)

• POLYBRAIN_DEBUG - Enable debug logging to stderr

• POLYBRAIN_CONFIG_PATH - Custom config file path

YAML Config Fields

httpPort: 32701                    # Optional
truncateLimit: 500                 # Optional
logLevel: info                      # Optional

models:                             # Required
  - id: "model-id"                 # Internal ID
    modelName: "actual-model-name"  # API model name
    baseUrl: "https://api.url/v1"  # API endpoint
    apiKey: "key or ${ENV_VAR}"    # API key
    provider: "openai"              # Optional: provider type for reasoning support

Supported Providers

The provider field enables provider-specific features like extended thinking/reasoning. If not specified, reasoning parameters will not be passed to the API (safe default).

Examples:

• Use provider: "openai" for OpenAI API models (GPT-4, o-series)

• Use provider: "openrouter" for OpenRouter proxy service (supports 400+ models)

• Omit provider field if your endpoint doesn't support reasoning parameters

Example with reasoning:

models:
  - id: "gpt-o1"
    modelName: "o1"
    baseUrl: "https://api.openai.com/v1"
    apiKey: "${OPENAI_API_KEY}"
    provider: "openai"           # Enables reasoning support

  - id: "gpt-5.1"
    modelName: "openai/gpt-5.1"
    baseUrl: "https://openrouter.io/api/v1"
    apiKey: "${OPENROUTER_KEY}"
    provider: "openrouter"       # Enables reasoning support

To use reasoning, set reasoning: true in the chat tool call. If the model and provider support it, you'll receive both the response and reasoning content.

Development

Setup

pnpm install

Build

pnpm build

Lint & Format

pnpm lint
pnpm format

Type Check

pnpm type-check

Development Mode

pnpm dev

Project Structure

src/
├── bin/polybrain.ts    # CLI entry point
├── launcher.ts         # Server launcher & management
├── http-server.ts      # HTTP server
├── index.ts            # Main server logic
├── mcp-tools.ts        # MCP tool definitions
├── conversation-manager.ts
├── openai-client.ts
├── config.ts
├── logger.ts
└── types.ts

Debugging

Enable debug logs to stderr:

{
  "mcpServers": {
    "polybrain": {
      "command": "polybrain",
      "env": {
        "POLYBRAIN_DEBUG": "true"
      }
    }
  }
}

Restart Server

After changing configuration in ~/.polybrain.yaml, restart the HTTP backend server:

polybrain --restart

This kills the background HTTP server. The next time you use polybrain, it will automatically start a fresh server with the updated configuration.

License

MIT