llm-fallback-mcp

MCP server that completes prompts with automatic provider fallback across OpenAI, Anthropic Claude, and Google Gemini. Built for production: rate-limit aware, retries on transient failures, transparent attempt log.

Why

LLM APIs go down. They rate-limit you. One provider has an outage, the others usually don't. Production LLM apps need fallback. This server gives you the pattern as a single MCP tool.

• Try OpenAI → Anthropic → Gemini in order (configurable)
• Each provider retries once on 429 / 5xx / network errors with backoff
• Return first success with a full per-provider attempt log
• Skip providers without keys automatically
• Zero SDK dependencies — calls each provider's REST API directly

Install

npm install -g llm-fallback-mcp

Or npx:

npx llm-fallback-mcp

Use with Claude Desktop

Add to claude_desktop_config.json (Windows: %APPDATA%\Claude\claude_desktop_config.json):

{
  "mcpServers": {
    "llm-fallback": {
      "command": "npx",
      "args": ["-y", "llm-fallback-mcp"],
      "env": {
        "OPENAI_API_KEY": "sk-...",
        "ANTHROPIC_API_KEY": "sk-ant-...",
        "GEMINI_API_KEY": "..."
      }
    }
  }
}

Only set keys for providers you want active. Missing keys = provider skipped.

Tools

complete

Arg	Type	Required	Default
prompt	string	yes	—
chain	string[]	no	["openai", "anthropic", "gemini"]
model_overrides	object	no	—
temperature	number	no	0.5
max_tokens	number	no	1024

health_check

Returns which providers are configured.

Example response

{
  "text": "...",
  "provider_used": "anthropic",
  "model_used": "claude-haiku-4-5-20251001",
  "attempts": [
    { "provider": "openai", "ok": false, "status": 429, "durationMs": 412 },
    { "provider": "anthropic", "ok": true, "durationMs": 1133 }
  ]
}

Local development

git clone https://github.com/KhushalB25/llm-fallback-mcp.git
cd llm-fallback-mcp
npm install
npm run build
OPENAI_API_KEY=sk-... npm start

Author

Khushal Bhandari · GitHub

License

MIT