@mctx-ai/dev

mctx — The best way to Build an MCP Server. Hot reload, request logging, and more — part of the mctx framework.

Quick Start

npm install -D @mctx-ai/dev
npx mctx-dev index.js

Your server restarts automatically on file changes.

What It Does

• Hot reload — watches .js, .mjs, .cjs, and .json files and restarts on save
• Request logging — logs every MCP request and response to the console
• Handler log surfacing — prints any log.*() calls made inside your handlers to the dev console after each request
• Sampling stub — when a tool calls ask(), the /_mctx/sampling endpoint returns a clear error explaining that sampling is not supported in dev mode
• Local testing — serves your server over HTTP for use with any MCP client

Usage

npx mctx-dev <entry-file> [options]

Options:

| Flag | Description | Default | | ----------------- | ----------------- | ------- | | --port <number> | Port to listen on | 3000 | | -h, --help | Show help message | |

Environment Variables:

| Variable | Description | | -------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | PORT | Port to listen on (overridden by --port) | | MCTX_VERBOSE | Set to true to pretty-print full JSON request and response bodies to stdout for every non-handshake MCP method call. Default (unset): compact one-line logs showing direction, status, and timing only. |

Examples:

# Start on default port 3000
npx mctx-dev index.js

# Start on a custom port
npx mctx-dev index.js --port 8080

Visual Testing

Use MCP Inspector to test your server interactively in the browser while mctx-dev is running.

Pairs With

This package is the dev companion to @mctx-ai/mcp — the zero-dependency MCP framework.