clap-mcp

# clap-mcp <div align="center"> <img src="logo.svg" width="200" height="200" alt="clap-mcp logo"> </div> Turn any Clap CLI into an MCP server with a simple derive macro. ## Installation ```toml [dependencies] clap-mcp = "0.1" ``` ## Quick Start Here's a complete calculator example that works as both a CLI and MCP server: ```rust use clap::{Parser, Subcommand}; use clap_mcp::McpMode; #[derive(Parser, McpMode)] #[command(name = "calculator")] #[command(about = "A simple calculator CLI that can also run as an MCP server")] struct Cli { #[command(subcommand)] command: Option<Commands>, /// Run as MCP server instead of CLI #[arg(long)] #[mcp(mode_flag)] mcp: bool, /// Port to run MCP HTTP server on (if not specified, uses stdio) #[arg(long, value_name = "PORT")] mcp_port: Option<u16>, } #[derive(Subcommand, Clone)] enum Commands { /// Add two numbers Add { #[arg(short, long)] a: f64, #[arg(short, long)] b: f64, }, /// Multiply two numbers Multiply { #[arg(long)] value1: f64, #[arg(long)] value2: f64, }, } fn execute_command(cmd: Commands) -> Result<String, String> { match cmd { Commands::Add { a, b } => { Ok(format!("{} + {} = {}", a, b, a + b)) } Commands::Multiply { value1, value2 } => { Ok(format!("{} * {} = {}", value1, value2, value1 * value2)) } } } fn main() -> Result<(), Box<dyn std::error::Error>> { let cli = Cli::parse(); if cli.mcp { // Run as MCP server - automatically exposes all commands as tools if let Some(port) = cli.mcp_port { // HTTP server mode on specified port let addr = format!("127.0.0.1:{}", port).parse()?; cli.run_mcp_server_http_with_handler(addr, execute_command)?; } else { // stdio mode (default) cli.run_mcp_server_with_handler(execute_command)?; } } else { // Run as normal CLI match execute_command(cli.command.expect("Subcommand required")) { Ok(output) => println!("{}", output), Err(e) => eprintln!("Error: {}", e), } } Ok(()) } ``` Now your CLI works both ways: ```bash # Traditional CLI mode $ calculator add -a 10 -b 32 10 + 32 = 42 $ calculator multiply --value1 7 --value2 6 7 * 6 = 42 # MCP server mode (stdio) $ calculator --mcp # Server is now running, ready for MCP clients to connect # MCP server mode (HTTP on specific port) $ calculator --mcp --mcp-port 8080 # Server running on http://127.0.0.1:8080, ready for HTTP-based MCP clients ``` ## Real Example: Cast Here's how you'd make Cast (Foundry's CLI) work as an MCP server: ```rust #[derive(Parser, McpMode)] struct Cast { #[command(subcommand)] cmd: CastCommand, #[arg(long)] #[mcp(mode_flag)] mcp: bool, } // That's it. All Cast commands are now available as MCP tools. ``` ## How It Works The `#[derive(McpMode)]` macro: - Adds a `run_mcp_server()` method to your CLI - Converts each subcommand into an MCP tool - Maps CLI arguments to tool parameters with proper types - Preserves all existing CLI functionality ## License MIT OR Apache-2.0