OpenRouter Fusion — MCP server

A tiny MCP server that exposes OpenRouter Fusion (multi-model deliberation) to any MCP client (MCPHub, Claude Desktop, Claude Code, …) when you need a very good answer.

What is Fusion? It turns your prompt into a small multi-model deliberation: a panel of models answers in parallel (with web search/fetch), then a judge ("Fuse with") model synthesizes consensus, contradictions, unique insights and blind spots into one final answer. It beats any single model on hard questions — at roughly 4–5× the cost of a single completion. Docs: https://openrouter.ai/docs/guides/features/plugins/fusion · model page: https://openrouter.ai/openrouter/fusion

Tools (v2 — async only)

The old synchronous wrappers (fusion_quality / fusion_ultra / fusion_perso) were removed — sync calls were cut by client/proxy timeouts. Everything goes through fusion_start + fusion_result.

fusion_start({ prompt, preset:"quality" }) → { job_id }
fusion_result({ job_id }) → answer   (re-call while {status:"running"})

fusion_start forces the deliberation pipeline (tool_choice:"required"). Per-call overrides: preset, reasoning_effort, temperature, analysis_models, judge_model, system.

Related MCP server: Wisepanel MCP Server

Configs (Quality / Budget / Custom)

Mirrors OpenRouter's "Model Fusion" UI tabs. Two are built-in in server.mjs; the rest are named custom configs, one per environment variable.

Each config carries analysis_models (panel) · judge (orchestrator) · reasoning_effort (xhigh|high|medium|low|minimal|none, default high) · temperature (null = model default, or 0–2) · optional system.

Configuring — one env var per config

The server scans every OPENROUTER_FUSION_<NAME> env var and registers it as a config named <name> (lowercased; override with a name field — e.g. code-eco). The value is the JSON object {...}; the parser also tolerates a "name":{...} fragment or a {"name":{...}} wrapper.

OPENROUTER_FUSION_MATHS    = {"name":"maths","analysis_models":[...],"judge":"...","reasoning_effort":"high","temperature":null,"system":"..."}
OPENROUTER_FUSION_CODE     = {...}
OPENROUTER_FUSION_PERSO    = {...}

• fusion-presets.json — canonical, documented copy of all configs.

• fusion-env-vars.json — the exact compact values to paste into the mcphub env (one per config).

• Extra vars: OPENROUTER_API_KEY (an inference key with credit), OPENROUTER_FUSION_DEFAULT_REASONING.

• Legacy OPENROUTER_FUSION_PRESETS (single map) and OPENROUTER_FUSION_PERSO_CONFIG are still read for backward-compat.

Diagnostic: FUSION_DUMP_PRESETS=1 node server.mjs prints the resolved configs and exits.

Install

npm install

No build step — plain ESM (node server.mjs). Requires Node ≥ 18 (global fetch).

Set your key via the client's env, or copy .env.example → .env:

OPENROUTER_API_KEY=sk-or-...

Use with MCPHub

Add a stdio server pointing at the absolute path of server.mjs:

{
  "name": "openrouter-fusion",
  "config": {
    "type": "stdio",
    "command": "node",
    "args": ["/absolute/path/to/openrouter-fusion/server.mjs"],
    "env": {
      "OPENROUTER_API_KEY": "sk-or-xxxxxxxxxxxxxxxx",
      "OPENROUTER_FUSION_MATHS": "{...}",
      "OPENROUTER_FUSION_CODE": "{...}"
    }
  }
}

If node isn't on the launching process's PATH, replace "node" with an absolute path.

Use with Claude Code / Claude Desktop

claude mcp add openrouter-fusion -e OPENROUTER_API_KEY=sk-or-... -- node "/absolute/path/to/server.mjs"

Example global slash commands you can drop into ~/.claude/commands/ (not shipped in this repo): /fusion & /fusion-choose (a selector that calls fusion_list then runs your pick), /fusion-quality, /fusion-budget, /fusion-custom <name> <question> — each just calls fusion_start with the matching preset then polls fusion_result.

Optional — package as a one-click .mcpb bundle

npx @anthropic-ai/mcpb pack

The bundle prompts the user for their OpenRouter API key on install (user_config).

Examples

// start a quality deliberation
{ "prompt": "Explain the trade-offs between ridge, lasso and elastic net.", "preset": "quality" }

// a custom config with a per-call reasoning override
{ "prompt": "Review this clinical case and list differential diagnoses.", "preset": "medecine", "reasoning_effort": "xhigh" }

Notes

• Model slugs use OpenRouter syntax — pick valid slugs from https://openrouter.ai/models.

• Fusion is billed per the panel + judge it runs — quality ($0.09 on a trivial probe) costs more than budget ($0.04). Keep the heavy configs for the cases that justify them.

• A tool-set change only shows client-side after the connector reconnects (cached manifest); calls still hit the live server.

• Jobs live in memory only. If the server process restarts, in-flight job_ids become Unknown — just call fusion_start again. Finished jobs are pruned after ~30 min (and on a background timer).