Model-agnostic MCP router for the Big Three: OpenAI, Claude, and Gemini.

One API, one UI — point any MCP server at any frontier model. Switch between GPT-5, Claude Opus 4, and Gemini 2.5 Pro without changing your tool integrations.

┌─────────────┐     ┌──────────────────────┐     ┌───────────────┐
│   Chat UI   │────▶│   POST /api/chat     │────▶│  MCP Servers  │
│  (browser)  │◀────│   Model Router       │◀────│  (any remote) │
└─────────────┘     └──────────────────────┘     └───────────────┘
                           │
                    ┌──────┼──────┐
                    ▼      ▼      ▼
               ┌────────┐ ┌─────┐ ┌────────┐
               │ OpenAI │ │Claude│ │ Gemini │
               │Response│ │ Msg │ │ GenAI  │
               │  API   │ │ API │ │  SDK   │
               └────────┘ └─────┘ └────────┘

The router detects the provider from the model string:

• gpt-*, o3*, o4* → OpenAI
• claude-* → Anthropic
• gemini-* → Google

Or use explicit prefixes: openai/gpt-4.1, anthropic/claude-sonnet-4-5, google/gemini-2.5-flash

Add environment variables for the providers you want to use:

You only need keys for providers you plan to use. The UI shows which are configured.

In the sidebar, add any remote MCP server URL. Examples:

• Val Town MCP: https://www.val.town/mcp
• Notion MCP: https://mcp.notion.com/mcp
• Any Streamable HTTP or SSE MCP server

Pick a model, type a message. The router handles the rest.

{
  "model": "gpt-4.1-mini",
  "messages": [
    { "role": "user", "content": "What tools do you have?" }
  ],
  "mcpServers": [
    { "url": "https://mcp.example.com/sse", "label": "my-server" }
  ],
  "system": "You are a helpful assistant."
}

Response (same shape for all providers):

{
  "content": "I have access to the following tools...",
  "toolCalls": [
    {
      "name": "list_tools",
      "serverLabel": "my-server",
      "arguments": "{}",
      "output": "..."
    }
  ],
  "provider": "openai",
  "model": "gpt-4.1-mini",
  "usage": { "inputTokens": 150, "outputTokens": 89 }
}

Returns available models and which API keys are configured.

• gpt-5 — GPT-5 flagship
• gpt-4.1 / gpt-4.1-mini / gpt-4.1-nano — GPT-4.1 family
• o3 / o4-mini — Reasoning models

• claude-opus-4-6 — Claude Opus 4
• claude-sonnet-4-5-20250929 — Claude Sonnet 4.5
• claude-haiku-3-5-20241022 — Claude Haiku 3.5

• gemini-2.5-pro — Gemini 2.5 Pro
• gemini-2.5-flash — Gemini 2.5 Flash
• gemini-2.0-flash — Gemini 2.0 Flash

OpenAI is the simplest: their Responses API handles MCP server-side. You pass a URL, they call the MCP server, execute tools, and return results. Zero orchestration code needed.

Anthropic and Google require client-side MCP orchestration. The router connects to MCP servers, discovers tools, converts schemas to each provider's format, then runs an agentic loop — sending messages, catching tool calls, executing them against MCP servers, and feeding results back until the model is done.

• Runtime: Val Town (Deno)
• Framework: Hono
• OpenAI: openai npm package — Responses API
• Anthropic: @anthropic-ai/sdk — Messages API
• Google: @google/genai — GenAI SDK
• MCP: @modelcontextprotocol/sdk — Streamable HTTP client

Built on Val Town. March 2026.