Switchback

MCP server for Switchback — classify AI agent turns by complexity and pick the cheapest model that can handle them. Drop-in for Claude Desktop, Cursor, Cline, and any MCP client.

npm Powers VibeKit

Built by VibeKit — same cascade router that powers every "Auto" turn in our hosted product. Learn more →

What it does

Exposes two tools over the Model Context Protocol:

• classify_turn — given a user message, returns {tier: 0|1|2, why, fallback, durationMs}. Use it when you're deciding whether to spend on a flagship model or stay on a cheap one for the next agent step.
• recommend_model — given a user message + a ladder of models (cheap → flagship), returns the cheapest model on the ladder that can plausibly handle it. Convenience wrapper around classify_turn.

Both tools fire a single small-model call via OpenRouter (default: openai/gpt-5.4-mini, ~$0.0001/call). Fail-soft: any error returns tier 1 with fallback: true rather than blocking your agent.

Install

npm install -g vibekit-switchback-mcp

Configure

Set your OpenRouter key (get one at https://openrouter.ai/keys):

export OPENROUTER_API_KEY=sk-or-...

Optional: override the classifier model:

export SWITCHBACK_CLASSIFIER_MODEL=anthropic/claude-haiku-4.5

Claude Desktop

Add to your ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "switchback": {
      "command": "npx",
      "args": ["-y", "vibekit-switchback-mcp"],
      "env": {
        "OPENROUTER_API_KEY": "sk-or-..."
      }
    }
  }
}

Cursor / Cline / others

Any MCP client that supports stdio servers. Same npx invocation.

Example calls

classify_turn:

{
  "userMessage": "rebuild the auth flow with passkeys"
}

returns:

{
  "tier": 2,
  "why": "architectural rework + new auth method",
  "fallback": false,
  "durationMs": 412
}

recommend_model:

{
  "userMessage": "fix typo in README",
  "ladder": [
    "openai/gpt-5.4-mini",
    "openai/gpt-5.4",
    "openai/gpt-5.5"
  ]
}

returns:

{
  "recommended_model": "openai/gpt-5.4-mini",
  "tier": 0,
  "ladder_size": 3,
  "classifier": { "tier": 0, "why": "trivial copy edit", "fallback": false, "durationMs": 318 }
}

When to use it

• Multi-step agents where you can swap models between rounds.
• BYOK-style products where you want to keep all routing inside the user's chosen brand — pass a brand-locked ladder per user.
• Cost-conscious orchestrators that want to avoid spending flagship rates on trivial turns.

When NOT to use it

• One-shot chat completions where you can't change models after the first call — use OpenRouter's auto or NotDiamond/Martian instead.
• Latency-critical sub-200ms-first-token UX — the classifier adds 200-500ms.

License

MIT. See LICENSE.

Built by VibeKit. The core library is vibekit-switchback — this package is the MCP wrapper.