llm-as-judge-mcp-server

The LLM as Judge MCP Server enables users of LLMs to get a second opinion for an LLM's response. The MCP tool sends the user's question, the LLM's response, and an optional focus for the evaluation to a second LLM for evaluation. This second opinion can be used to then improve an LLM's response and give users another perspective regarding the original LLM's response.

Installation

You can run this MCP server using node with the following command. This can also be used in MCP configuration files, which can be seen in the setup section below.

npx -y @jgsheppa/llm-as-judge-mcp-server

You can also download a binary which matches your machine's architecture to start using llm-as-judge-mcp-server.

Setup

To set up the llm-as-judge-mcp-server, you can define the MCP server in a JSON file wherever your LLM has access to MCP servers.

{
  "mcpServers": {
    "llm-as-judge": {
      "command": "npx",
      "args": [
        "-y",
        "@jgsheppa/llm-as-judge-mcp-server",
        "stdio",
        "-p", 
        "gemini", 
        ],
      "env": {
        "GEMINI_API_KEY": "your-api-key",
      }
    },
  }
}

To customize your model and prompt, you configuration would look like this:

{
  "mcpServers": {
    "llm-as-judge": {
      "command": "npx",
      "args": [
        "-y",
        "@jgsheppa/llm-as-judge-mcp-server",
        "stdio",
        "-p", 
        "gemini", 
        "-m", 
        "gemini-2.5-flash", 
        "--prompt-path",
        "/Users/firstlast/Desktop/PROMPT.md"
        ],
      "env": {
        "GEMINI_API_KEY": "your-api-key",
      }
    },
  }
}

To define your provider and model, you can pass them as arguments to the MCP server. And while there is a default prompt for the LLM as judge, you can also pass your own custom prompt by providing the full filepath to the --prompt-path argument.

Features

Providers

Currently three providers are available for this MCP server:

• Anthropic
• Gemini
• Ollama
• OpenAI

More providers can and will be added in the future.

Models

Any models offered by the previously mentioned providers can be used as LLM judges. It is up to you to decide which model works best for your use-case, but a bigger, frontier model is not necessarily the best option to evaluate the response of another frontier model. Smaller, less expensive models can be great options as well.

Default Models

To try and improve the experience of using this MCP server, there are default models for each provider. The models were chosen because they are the most cost-efficient. These might change in the future, but since they are customizable, these seem like fine choices for now.

| Provider | Default Model | |-----------|-------------------| | Anthropic | claude-haiku-4-5 | | Gemini | gemini-2.5-flash | | Ollama | gemma3:4b | | OpenAI | gpt-5-mini |

Prompts

This MCP server offers a default prompt for an LLM to evaluate another LLM's response, but you can also provide your own prompt for further customization.