mcplug

A Rust toolkit for discovering, calling, and composing Model Context Protocol (MCP) servers — as a CLI tool and library crate.

No Node.js required. No npx. Just a single native binary.

Features

• Discover MCP servers configured in Cursor, Claude Desktop, Claude Code, VS Code, Windsurf, Codex, and OpenCode
• Call any MCP tool from the command line with flexible argument formats
• OAuth browser-based authentication for protected MCP servers
• Daemon mode for persistent background server connections
• Code generation — emit Rust types or standalone CLI binaries from MCP server schemas
• Library crate — embed MCP tool calling in your own Rust applications

Installation

cargo install --path .

Or build from source:

cargo build --release

Quick Start

List configured servers

mcplug list

List tools on a specific server

mcplug list firecrawl

Call a tool

mcplug call firecrawl.crawl url:https://example.com

Shorthand (infers call):

mcplug firecrawl.crawl url:https://example.com

Function-call syntax:

mcplug call 'firecrawl.crawl(url: "https://example.com")'

Ad-hoc connections (no config needed)

# HTTP/SSE endpoint
mcplug list --http-url https://mcp.example.com/mcp

# stdio server
mcplug list --stdio "npx -y some-mcp-server"

Configuration

mcplug reads config from these locations (highest precedence first):

1. --config <path> CLI flag
2. MCPLUG_CONFIG environment variable
3. ./config/mcplug.json (project-level)
4. ~/.mcplug/mcplug.json (home-level)

It also reads mcporter config files as a fallback for migration.

Config format

{
  "mcpServers": {
    "firecrawl": {
      "baseUrl": "https://mcp.firecrawl.dev/mcp",
      "headers": { "Authorization": "$env:FIRECRAWL_API_KEY" }
    },
    "local-tool": {
      "command": "my-mcp-server",
      "args": ["--port", "3000"]
    }
  },
  "imports": ["cursor", "claude-code", "claude-desktop"]
}

Editor imports

mcplug auto-discovers MCP servers configured in your editors:

CLI Commands

Use --json on any command for machine-readable output.

Library Usage

Add to your Cargo.toml:

[dependencies]
mcplug = { path = "." }

One-shot call

use mcplug::call_once;

let result = call_once("firecrawl", "crawl", json!({"url": "https://example.com"})).await?;
println!("{}", result.text());

Runtime with connection pooling

use mcplug::Runtime;

let runtime = Runtime::from_config().await?;
let result = runtime.call_tool("context7", "resolve-library-id", json!({"libraryName": "react"})).await?;
runtime.close().await?;

Typed server proxy

use mcplug::{Runtime, ServerProxy};

let runtime = Runtime::from_config().await?;
let chrome = ServerProxy::new(&runtime, "chrome-devtools");
let snapshot = chrome.call("takeSnapshot", json!({})).await?;

Testing

cargo test               # run all tests (unit + integration)
cargo test --lib         # unit tests only
cargo test --test cli_integration  # specific integration suite

304 tests covering all modules: argument parsing, config loading/merging, CLI commands, OAuth flow, transports (stdio + HTTP), runtime connection pooling, daemon management, code generation, and error handling.

Integration tests use a mock MCP server binary (tests/fixtures/mock_mcp_server.rs) that supports 5 tools over stdio. CLI tests use assert_cmd for end-to-end binary verification.

Environment Variables

Claude Code Plugin

mcplug ships with a Claude Code plugin that provides contextual help when working on or with the project.

claude --plugin-dir /path/to/mcplug

This enables:

• Skills — contextual knowledge about CLI commands, configuration, and library API (activated automatically by relevant questions)
• Commands — /mcplug:quickstart for first-run setup, /mcplug:troubleshoot for diagnosing issues
• Agent — mcplug-guide answers questions like "how do I use mcplug" by consulting skills and source code

Acknowledgements

mcplug is inspired by mcporter, a Node.js-based MCP tool runner. mcplug aims to bring the same capabilities to the Rust ecosystem as a single native binary with no Node.js dependency.

License

MIT