MCP Node.js Debugger

Created By

hyperdrive-eng9 months ago

✸ MCP Node.js debugger

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

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

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

Run a Node.js server in debug mode (i.e. with the --inspect flat)
```
node --inspect {file.js}
```
Ask Cursor to debug your Node.js server at runtime

Claude Code

Add to Claude Code

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

Start Claude Code

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

Run a Node.js server in debug mode (i.e. with the --inspect flat)
```
# In another terminal
node --inspect {file.js}
```

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

Add to Claude Code

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

Verify connection

> /mcp
  ⎿  MCP Server Status

     • nodejs-debugger: connected

Remove from Claude Code
```
claude remove nodejs-debugger
```

Cursor

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

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

Verify connection:

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

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

Example

Cursor

Run this simple Node.js app: github.com/mdn/express-locallibrary-tutorial:
```
node --inspect ./bin/www
```
Ask Cursor to set a breakpoint
Create a book at localhost:3000/catalog/book/create
Watch Cursor capture runtime state

Claude Code

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
}

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:coolpassword@cluster0.cojoign.mongodb.net/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:coolpassword@cluster0.cojoign.mongodb.net/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?