MCP Server Connection Issue - Server Disconnects Immediately After Initialization

[garciasdos]

Description

The MCP server initializes successfully but immediately disconnects, preventing the extension from functioning properly in Claude.

Expected Behavior

The MCP server should maintain a stable connection after initialization and remain available for use.

Actual Behavior

• Server starts and connects successfully
• Receives initialization message from client
• Server transport closes unexpectedly immediately after
• Connection terminates with "Server disconnected" error
• Extensions seems to be correctly installed:

Error Details

Environment

• Platform: MacOS 15.5 (24F74)
• Node.js version: (Built-in) 22.15.0
• Claude Desktop version: 0.11.6 (0aa9ce)

Logs

2025-07-04T14:24:26.513Z [Postman API MCP] [info] Initializing server... { metadata: undefined }
2025-07-04T14:24:26.526Z [Postman API MCP] [info] Using built-in Node.js for MCP server: Postman API MCP { metadata: undefined }
2025-07-04T14:24:26.528Z [Postman API MCP] [info] Server started and connected successfully { metadata: undefined }
2025-07-04T14:24:26.545Z [Postman API MCP] [info] Message from client: {"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0} { metadata: undefined }
2025-07-04T14:24:26.812Z [Postman API MCP] [info] Server transport closed { metadata: undefined }
2025-07-04T14:24:26.812Z [Postman API MCP] [info] Client transport closed { metadata: undefined }
2025-07-04T14:24:26.812Z [Postman API MCP] [info] Server transport closed unexpectedly, this is likely due to the process exiting early. If you are developing this MCP server you can add output to stderr (i.e. console.error('...') in JavaScript, print('...', file=sys.stderr) in python) and it will appear in this log. { metadata: undefined }
2025-07-04T14:24:26.812Z [Postman API MCP] [error] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging) { metadata: { context: 'connection', stack: undefined } }
2025-07-04T14:24:26.812Z [Postman API MCP] [info] Client transport closed { metadata: undefined }

Manifest.json

{
  "$schema": "../../dist/dxt-manifest.schema.json",
  "dxt_version": "0.1",
  "name": "postman-api-mcp",
  "display_name": "Postman API MCP",
  "version": "1.0.0",
  "description": "A simple MCP server to operate on the Postman API",
  "long_description": "This extension allows AI assistants to interact with the Postman API through the Model Context Protocol (MCP). It provides a rich set of tools for managing collections, environments, mocks, monitors, and more, all secured with the user's Postman API key.",
  "author": {
    "name": "Postman, Inc.",
    "email": "help@postman.com",
    "url": "https://www.postman.com"
  },
  "repository": {
    "type": "git",
    "url": "https://github.com/postmanlabs/postman-api-mcp"
  },
  "homepage": "https://github.com/postmanlabs/postman-api-mcp",
  "documentation": "https://learning.postman.com/docs/postman-ai-agent-builder/",
  "support": "https://github.com/postmanlabs/postman-api-mcp/issues",
  "icon": "icon.png",
  "server": {
    "type": "node",
    "entry_point": "src/index.js",
    "mcp_config": {
      "command": "node",
      "args": [
        "${__dirname}/src/index.js"
      ],
      "env": {
        "POSTMAN_API_KEY": "${user_config.postman_api_key}"
      }
    }
  },
  "keywords": [
    "postman",
    "api",
    "mcp",
    "postman-api",
    "collections",
    "monitors",
    "mocks"
  ],
  "license": "Apache-2.0",
  "user_config": {
    "postman_api_key": {
      "type": "string",
      "title": "Postman API Key",
      "description": "Your Postman API key used for authenticating requests",
      "sensitive": true,
      "required": true
    }
  },
  "compatibility": {
    "claude_desktop": ">=0.10.0",
    "platforms": [
      "darwin",
      "win32",
      "linux"
    ],
    "runtimes": {
      "node": ">=20.0.0"
    }
  },
  "tools_generated": true
}

Troubleshooting Attempted

• Verified all dependencies are installed
• Checked for required configuration files
• Confirmed file permissions
• Attempted manual server execution
• Reviewed extension documentation

What am I missing here?

[alfonsograziano]

Hi, I'm currently experiencing the same issue. In case you find a solution, please let me know

Here my PR with the Manifest: alfonsograziano/node-code-sandbox-mcp#94

2025-07-04T18:43:16.327Z [node-code-sandbox] [info] Initializing server... { metadata: undefined }
2025-07-04T18:43:16.333Z [node-code-sandbox] [info] Using built-in Node.js for MCP server: node-code-sandbox { metadata: undefined }
2025-07-04T18:43:16.337Z [node-code-sandbox] [info] Server started and connected successfully { metadata: undefined }
2025-07-04T18:43:16.349Z [node-code-sandbox] [info] Message from client: {"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0} { metadata: undefined }
2025-07-04T18:43:16.668Z [node-code-sandbox] [info] Server transport closed { metadata: undefined }
2025-07-04T18:43:16.669Z [node-code-sandbox] [info] Client transport closed { metadata: undefined }
2025-07-04T18:43:16.669Z [node-code-sandbox] [info] Server transport closed unexpectedly, this is likely due to the process exiting early. If you are developing this MCP server you can add output to stderr (i.e. `console.error('...')` in JavaScript, `print('...', file=sys.stderr)` in python) and it will appear in this log. { metadata: undefined }
2025-07-04T18:43:16.669Z [node-code-sandbox] [error] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging) { metadata: { context: 'connection', stack: undefined } }
2025-07-04T18:43:16.669Z [node-code-sandbox] [info] Client transport closed { metadata: undefined }

[alfonsograziano]

Personal update: I have NVM and I had a lot of version installed (from v14 to v23).
My Claude Desktop installation has v22.15.1 installed.

I disabled the "Use Built-in Node.js for MCP", and I had to uninstall all the versions from v14 up to v21. Now it's using v23 and it's working.

I'm not sure if this might fix your problem as well. I'll try to build my project so that it's compatible with older versions of Node.js as well.

[DanielSinclair]

Same issue here. I tried the above with different system Node versions, but to no avail. The same bundle runs perfectly with node index.js from the command line. It seems like stdout is also not being captured by the logger. Unsure how to debug!

2025-07-08T20:41:29.261Z [Rainbow CMS] [info] Initializing server... { metadata: undefined }
2025-07-08T20:41:29.282Z [Rainbow CMS] [info] Using built-in Node.js for MCP server: Rainbow CMS { metadata: undefined }
2025-07-08T20:41:29.294Z [Rainbow CMS] [info] Server started and connected successfully { metadata: undefined }
2025-07-08T20:41:29.311Z [Rainbow CMS] [info] Message from client: {"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0} { metadata: undefined }
2025-07-08T20:41:29.559Z [Rainbow CMS] [info] Server transport closed { metadata: undefined }
2025-07-08T20:41:29.559Z [Rainbow CMS] [info] Client transport closed { metadata: undefined }
2025-07-08T20:41:29.559Z [Rainbow CMS] [info] Server transport closed unexpectedly, this is likely due to the process exiting early. If you are developing this MCP server you can add output to stderr (i.e. `console.error('...')` in JavaScript, `print('...', file=sys.stderr)` in python) and it will appear in this log. { metadata: undefined }
2025-07-08T20:41:29.559Z [Rainbow CMS] [error] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging) { metadata: { context: 'connection', stack: undefined } }
2025-07-08T20:41:29.559Z [Rainbow CMS] [info] Client transport closed { metadata: undefined }

[alfonsograziano]

@DanielSinclair please, do you mind to try and disable the built-in Node.js for MCP from the settings? And ensure that the version that is available in the UI is one that is supported from your project (as I had a few versions installed, somehow it defaulted to the older one).

That did the trick for me, but I don't feel comfortable sending the Extension for review at the moment until this is sorted out. I'd love to find a proper solution leveraging the built-in node version.

(and yes, my project is compatible with the version they're supposed to use in Claude Desktop, as I installed that version and locally works perfectly, as you mentioned as well)

[DanielSinclair]

@alfonsograziano Yes, have tried that and shifted my default version to v18, v22, and v23 via nvm. Runs perfectly from command line, but fails as a DXT. No luck thus far.

[oshchyhol]

Running into the same issue in Claude 0.12.16 (fae442) 2025-07-14T19:10:28.000Z
Looks like this is also currently affecting a lot of published extensions, including Stripe.

I looked at a couple of OSS ones. For instance, PDF Filler fails with the same error, while Spotify (Applescript) works fine.

[kapravel]

Same for Socket. The bundled nodejs crashes at the beginning without any output in the logs. If I don't use the build-in nodejs binary (22.15.1) but the same version installed on the system with nvm then it works.

It would be great to know exactly how the server is started with the build-in nodejs (so that we can reproduce the errors). It would also help if process invocation errors show up in the mcp.log.

[MarshallOfSound]

Hey folks, if you were experiencing this issue can you try updating to Claude Desktop 0.12.20 (the latest release).

[alfonsograziano]

@MarshallOfSound sounds good thanks, over the weekend I'll try to do it and if everything works I'll publish my package. Thanks for the support

[nickwinder]

I found I was still experiencing the issue on macOS with 0.12.20.
In the end, I worked out it was to do with the variable replacement my manifest.json specified as the default.

...json
    "allowed_directories": {
      "type": "directory",
      "title": "Allowed Directories",
      "description": "Directories the server can access",
      "required": true,
      "default": "${HOME}"
    },
...

Once I removed the variable, and forced the user to browser to a directory using the UI, the error disappeared. For now, I've had to remove the variable replacement from the default.

[kapravel]

Hey folks, if you were experiencing this issue can you try updating to Claude Desktop 0.12.20 (the latest release).

I can confirm that 0.12.20 resolved the issue for the Socket MCP Server, it now loads correctly with the build-in nodejs binary. Thanks for the fix!

[MarshallOfSound]

@nickwinder That looks like it should work per spec, can you double check by running dxt validate against your manifest. If it says it's valid but still doesn't work can you raise a new issue and we can discuss that over there.

[garciasdos]

Hey @MarshallOfSound , dxt v0.2.5 with Claude 0.12.20 (29349a) 2025-07-17T16:38:53.000Z now launches the MCP Server. However, I encounter some errors when I start, even though the MCP eventually works;

2025-07-18T13:09:44.159Z [Postman API MCP] [error] Expected ',' or ']' after array element in JSON at position 5 (line 1 column 6) {
  metadata: {
    context: 'connection',
    stack: "SyntaxError: Expected ',' or ']' after array element in JSON at position 5 (line 1 column 6)\n" +
      '    at JSON.parse (<anonymous>)\n' +
      '    at F7e (/Applications/Claude.app/Contents/Resources/app.asar/.vite/build/index-CCX0UMdN.js:178:206)\n' +
      '    at D7e.readMessage (/Applications/Claude.app/Contents/Resources/app.asar/.vite/build/index-CCX0UMdN.js:178:133)\n' +
      '    at sW.processReadBuffer (/Applications/Claude.app/Contents/Resources/app.asar/.vite/build/index-CCX0UMdN.js:179:2098)\n' +
      '    at Socket.<anonymous> (/Applications/Claude.app/Contents/Resources/app.asar/.vite/build/index-CCX0UMdN.js:179:1652)\n' +
      '    at Socket.emit (node:events:518:28)\n' +
      '    at addChunk (node:internal/streams/readable:561:12)\n' +
      '    at readableAddChunkPushByteMode (node:internal/streams/readable:512:3)\n' +
      '    at Readable.push (node:internal/streams/readable:392:5)\n' +
      '    at Pipe.onStreamRead (node:internal/stream_base_commons:189:23)'
  }
}

The error also appears in the UI (again, this doesn't interfere with the MCP functioning);

Am I missing anything in the manifest? The MCP works fine in other clients.

[MarshallOfSound]

@garciasdos Your MCP server should not log anything as it may interfere with the custom transport wrapper, we attempt to intercept those log messages but it's possible you're accidentally logging things on the same output stream that powers the mcp transport. Is y'all DXT available anywhere for testing?