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MCP Node.js Debugger: Real-Time Insights & Smart Breakpoints - MCP Implementation

MCP Node.js Debugger: Real-Time Insights & Smart Breakpoints

MCP Node.js Debugger: Effortlessly track down bugs with real-time insights, smart breakpoints, and seamless integration – your code’s frustration-free superhero! 🚀

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About MCP Node.js Debugger

What is MCP Node.js Debugger: Real-Time Insights & Smart Breakpoints?

MCP Node.js Debugger is a server-side tool enabling real-time debugging of Node.js applications directly within AI development environments like Cursor and Claude Code. By integrating runtime insights and smart breakpoint capabilities, it bridges the gap between AI-driven analysis and live code execution. The tool allows developers to inspect variables, trace execution paths, and diagnose errors dynamically—without interrupting the application workflow.

How to Use MCP Node.js Debugger: Real-Time Insights & Smart Breakpoints?

Integrating the debugger involves three core steps:

  • Setup: Configure the MCP server in your IDE (Cursor/Claude Code) via JSON configuration or CLI commands.
  • Run in Debug Mode: Launch your Node.js app with the --inspect flag to enable debugging protocols.
  • Debug Interactively: Issue commands to set breakpoints, inspect runtime states, or trigger variable dumps through your AI assistant.

For example, with Cursor, add the MCP server to ~/.cursor/mcp.json and ask the assistant to "set a breakpoint at line X" during runtime.

MCP Node.js Debugger Features

Key Features of MCP Node.js Debugger: Real-Time Insights & Smart Breakpoints?

  • Live Variable Inspection: View the current value of variables, objects, and function outputs at any breakpoint.
  • Smart Breakpoint Logic: Automatically resolve file paths and line numbers, even in complex module structures.
  • IDE Integration: Seamless support for Cursor and Claude Code, with contextual debugging prompts tailored to your workflow.
  • Error Tracing: Automatically correlate runtime errors with specific code locations and suggest fixes based on live data.

Use Cases of MCP Node.js Debugger: Real-Time Insights & Smart Breakpoints?

Common scenarios include:

  • Diagnosing Database Connections: Like resolving MongoDB Atlas IP whitelisting issues by inspecting connection strings in real time.
  • API Request Analysis: Trace HTTP requests/responses through breakpoints to pinpoint malformed payloads or authentication failures.
  • Performance Bottlenecks: Monitor function execution times and memory usage without manual logging.

For instance, when encountering a Mongoose connection error, the debugger can log the actual MONGODB_URI

MCP Node.js Debugger FAQ

FAQ from MCP Node.js Debugger: Real-Time Insights & Smart Breakpoints?

  • Q: Does this work with any Node.js version?
    Supported on Node.js 16+ due to required debugging protocol features.
  • Q: Can I use it without an AI assistant?
    While designed for Cursor/Claude Code, the core MCP server can be adapted for custom CLI workflows.
  • Q: How are breakpoints managed across modules?
    The tool resolves relative paths and handles ES6 imports/exports automatically.
  • Q: Is there a performance overhead?
    Minimal—debugging pauses only occur when actively inspecting or stepping through code.

Content

MCP Node.js Debugger

An MCP server that gives Cursor or Claude Code access to Node.js at runtime to help you debug: @hyperdrive-eng/mcp-nodejs-debugger.

Demo

Cursor

https://github.com/user-attachments/assets/c193a17e-b0e6-4c51-82aa-7f3f0de17e1a

Claude Code

https://github.com/user-attachments/assets/adb7321b-3a6a-459b-a5c9-df365710d4d8

Quick start

Cursor

  1. Add to Cursor (~/.cursor/mcp.json)

image

    + {
+   "mcpServers": {
+   "nodejs-debugger": {
+      "command": "npx",
+       "args": ["@hyperdrive-eng/mcp-nodejs-debugger"]
+     }
+   }
+ }

  1. Run a Node.js server in debug mode (i.e. with the --inspect flat)

    node --inspect {file.js}

  2. Ask Cursor to debug your Node.js server at runtime

image

Claude Code

  1. Add to Claude Code

    claude mcp add nodejs-debugger npx @hyperdrive-eng/mcp-nodejs-debugger

  2. Start Claude Code

    claude

╭───────────────────────────────────────────────────────╮
│ ✻ Welcome to Claude Code research preview!            │
│                                                       │
│   /help for help                                      │
│                                                       │
│   Found 1 MCP server (use /mcp for status)            │
╰───────────────────────────────────────────────────────╯

  1. Run a Node.js server in debug mode (i.e. with the --inspect flat)

    In another terminal

node --inspect {file.js}

  1. Ask Claude Code to debug your Node.js server at runtime

    I'm getting a runtime error in Node.js

    {YOUR_RUNTIME_ERROR}

    Please help me debug this error at runtime using the nodejs-debugger mcp.

Usage

Claude Code

  1. Add to Claude Code

    claude mcp add nodejs-debugger npx mcp-nodejs-debugger

  2. Verify connection

    /mcp
    ⎿ MCP Server Status

    • nodejs-debugger: connected

  3. Remove from Claude Code

    claude remove nodejs-debugger

Cursor

  1. Add to Cursor (~/.cursor/mcp.json)

    • {
+   "mcpServers": {
+   "nodejs-debugger": {
+      "command": "npx",
+       "args": ["@hyperdrive-eng/mcp-nodejs-debugger"]
+     }
+   }
+ }
  1. Verify connection:

image

  1. Remove from Cursor (~/.cursor/mcp.json):

    • {
-   "mcpServers": {
-   "nodejs-debugger": {
-      "command": "npx",
-       "args": ["@hyperdrive-eng/mcp-nodejs-debugger"]
-     }
-   }
- }

Example

Cursor

  1. Run this simple Node.js app: github.com/mdn/express-locallibrary-tutorial:

    node --inspect ./bin/www

  2. Ask Cursor to set a breakpoint

image

image

  1. Create a book at localhost:3000/catalog/book/create

image

  1. Watch Cursor capture runtime state

image

Claude Code

  1. Here is a buggy Node.js server:

    node --inspect index.js

Debugger listening on ws://127.0.0.1:9229/2862f5a2-8618-4516-8429-1248b397e9b4

#######################
## THE RUNTIME ERROR ##
#######################
MongooseServerSelectionError: Could not connect to any servers in your MongoDB Atlas cluster. One common reason is that you're trying to access the database from an IP that isn't whitelisted. Make sure your current IP address is on your Atlas cluster's IP whitelist: https://www.mongodb.com/docs/atlas/security-whitelist/
    at _handleConnectionErrors (/Users/arthur/Documents/thirdparties/mdn/express-locallibrary-tutorial/node_modules/mongoose/lib/connection.js:1110:11)
    at NativeConnection.openUri (/Users/arthur/Documents/thirdparties/mdn/express-locallibrary-tutorial/node_modules/mongoose/lib/connection.js:1041:11)
    at async main (/Users/arthur/Documents/thirdparties/mdn/express-locallibrary-tutorial/app.js:35:3) {
  reason: TopologyDescription {
    type: 'ReplicaSetNoPrimary',
    servers: Map(3) {
      'ac-8e6hgk7-shard-00-01.cojoign.mongodb.net:27017' => [ServerDescription],
      'ac-8e6hgk7-shard-00-02.cojoign.mongodb.net:27017' => [ServerDescription],
      'ac-8e6hgk7-shard-00-00.cojoign.mongodb.net:27017' => [ServerDescription]
    },
    stale: false,
    compatible: true,
    heartbeatFrequencyMS: 10000,
    localThresholdMS: 15,
    setName: 'atlas-5syy8t-shard-0',
    maxElectionId: null,
    maxSetVersion: null,
    commonWireVersion: 0,
    logicalSessionTimeoutMinutes: null
  },
  code: undefined
}

  1. Claude Code debugs the Node.js server at runtime:

    I'm getting a runtime error connecting to mongoose. Please help me debug by checking the value of
    the mongodb configs at runtime using the nodejs-debugger mcp.

    ⏺ I'll help you debug the mongoose connection issue using the Node.js debugger. Let's first understand where the
    MongoDB connection is configured.

    ⏺ Search(pattern: "**/*.js")…
    ⎿  Found 100 files

    ⏺ Let's set a breakpoint at the mongoose connection point and continue:

    ⏺ nodejs-debugger:set_breakpoint (MCP)(file: …
    "/Users/arthur/Documents/thirdparties/mdn/express-locallibrary-tutorial/app.js",
    line: 35)
      ⎿  Breakpoint set successfully. ID:
    2:34:0:file:///Users/arthur/Documents/thirdparties/mdn/express-locallibrary-tutorial/app.js
    ⏺ Let's list all our breakpoints:

    ⏺ nodejs-debugger:list_breakpoints (MCP)
      ⎿  [
    {
    "file": "/Users/arthur/Documents/thirdparties/mdn/express-locallibrary-tutorial/app.js",
    "line": 35,
    "id": "2:34:0:file:///Users/arthur/Documents/thirdparties/mdn/express-locallibrary-tutorial/app\.js"
    }
    ]
    ⏺ Let's try to execute a specific piece of code to check the connection variables:

    ⏺ nodejs-debugger:nodejs_inspect (MCP)(js_code: "// Get the mongoose module and inspect connection\nconst mongoose = …
    require('mongoose');\nconsole.log('Current mongoose version:',
    mongoose.version);\nconsole.log('Current mongoose connection state:',
    mongoose.connection.readyState);\n// Log connection string safely (without
    password)\nconst connectionString = process.env.MONGODB_URI || \n
    "mongodb+srv://cooluser:[email protected]/local_library?retryWr
    ites=true&w=majority&appName=Cluster0";\nconsole.log('Connection string
    (masked):', connectionString.replace(/(?<=mongodb\+srv:\/\/\w+:)(.+?)(?=@)/,
    '*****'));")
      ⎿  Console output:
    [log] Current mongoose version: 8.9.5
    [log] Current mongoose connection state: 0
    [log] Connection string (masked): mongodb+srv://cooluser:[email protected]/local_library?retryWri
    tes=true&w=majority&appName=Cluster0
    ⏺ The runtime error you're seeing in your application is related to MongoDB
    Atlas connection issues. Based on your error message, the problem is:

    1. You're using placeholder credentials ("cooluser:coolpassword")

    To fix this, you have two options:

    1. Use a local MongoDB instance by changing line 29-30 in app.js to:
      const dev_db_url = "mongodb://127.0.0.1:27017/local_library";
    2. Or correctly set up MongoDB Atlas:
      - Log into Atlas at https://cloud.mongodb.com
      - Go to Network Access and add your current IP to whitelist
      - Create proper database credentials
      - Update the connection string with real credentials

    Which option would you like to proceed with?

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