An MCP server that gives Claude Code access to NodeJS at runtime to help you debug: mcp-nodejs-debugger.
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Add to Claude Code:
claude mcp add nodejs-debugger npx @hyperdrive-eng/mcp-nodejs-debugger
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Start Claude Code
claude ╭───────────────────────────────────────────────────────╮ │ ✻ Welcome to Claude Code research preview! │ │ │ │ /help for help │ │ │ │ Found 1 MCP server (use /mcp for status) │ ╰───────────────────────────────────────────────────────╯
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Run a NodeJS server in debug mode (i.e. with the
--inspectflat)# In another terminal node --inspect {your_file.js} -
Ask Claude Code to debug your NodeJS server at runtime
> I'm getting a runtime error in NodeJS. {YOUR_RUNTIME_ERROR} Please help me debug this error at runtime using the nodejs-debugger mcp.
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Add to Claude Code:
claude mcp add nodejs-debugger npx mcp-nodejs-debugger
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Verify connection
> /mcp ⎿ MCP Server Status • nodejs-debugger: connected -
Remove from Claude Code:
claude remove nodejs-debugger
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Here is a buggy NodeJS 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 NodeJS 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?