rs-cel-mcp: A CEL MCP Server

rs-cel-mcp is a server that implements the Model Context Protocol (MCP) to provide a Common Expression Language (CEL) evaluation tool to compatible clients, such as the Gemini CLI.

How to Run

1. Build the Server

First, build the project in release mode:

cargo build --release

2. Run the Server

Once built, you can start the server using the --http flag to specify the listening address and port:

./target/release/cel-mcp --http 127.0.0.1:1234

The server will now be running and listening for requests on http://127.0.0.1:1234.

How to Use with MCP Clients

You can connect this server to any MCP-compatible client. Here are instructions for two common clients.

Gemini CLI

To allow the Gemini CLI to use this server, you need to add the server's configuration to your settings.json file.

To avoid overwriting your existing settings, you should merge the following configuration into the mcpServers object in your settings.json.

{
  "mcpServers": {
    "cel-evaluator": {
      "httpUrl": "http://127.0.0.1:1234/mcp"
    }
  }
}

After adding the configuration and restarting the Gemini CLI, it will discover and be able to use the CEL evaluation tool.

ollmcp

You can also use this server with ollmcp, a TUI client for Ollama.

While the rs-cel-mcp server is running, open a new terminal and run ollmcp with the --mcp-server-url flag pointing to the server's address.

ollmcp --mcp-server-url http://127.0.0.1:1234/mcp --model qwen2.5:7b

This will start ollmcp and connect it to your CEL server, allowing the specified Ollama model to use the evaluate tool.