Unexpected end of JSON input

[daBee]

Describe the bug
Cannot connect & Errors on Claude Desktop launched.

2025-03-22T20:59:59.754Z [postgres] [info] Initializing server...
2025-03-22T20:59:59.786Z [postgres] [info] Server started and connected successfully
2025-03-22T20:59:59.814Z [postgres] [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}
2025-03-22T20:59:59.981Z [postgres] [error] Unexpected end of JSON input {"context":"connection","stack":"SyntaxError: Unexpected end of JSON input\n    at JSON.parse (<anonymous>)\n    at EPe (/Applications/RF_Utilities/Claude.app/Contents/Resources/app.asar/.vite/build/index.js:82:189)\n    at SPe.readMessage (/Applications/RF_Utilities/Claude.app/Contents/Resources/app.asar/.vite/build/index.js:82:115)\n    at TPe.processReadBuffer (/Applications/RF_Utilities/Claude.app/Contents/Resources/app.asar/.vite/build/index.js:83:1842)\n    at Socket.<anonymous> (/Applications/RF_Utilities/Claude.app/Contents/Resources/app.asar/.vite/build/index.js:83:1523)\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:191:23)"}
2025-03-22T20:59:59.988Z [postgres] [info] Server transport closed
2025-03-22T20:59:59.988Z [postgres] [info] Client transport closed
2025-03-22T20:59:59.988Z [postgres] [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.
2025-03-22T20:59:59.988Z [postgres] [error] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging) {"context":"connection"}
2025-03-22T20:59:59.989Z [postgres] [info] Client transport closed

To Reproduce
Steps to reproduce the behavior:

1. Startup Claude Desktop
2. Read Log

Expected behavior
I thought it would have the ability to connect properly. Errors up front and no working connection.

Logs
see above

Additional context
Checked the json in the config file and everything seems legit.

[ron-42]

Can you share MCP configuration file?

[daBee]

{
  "globalShortcut": "Ctrl+Space",
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": [
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "/Users/rich/Desktop",
        "/Users/rich/Downloads"
      ]
    },
    "postgres": {
      "command": "echo",
      "server": {
        "type": "tcp",
        "host": "192.168.1.23",
        "port": 5432,
        "timeout": 10000,
        "authentication": {
          "type": "postgres",
          "username": "richie",
          "password": "secretpassword",
          "database": "richie"
        }
      },
      "protocol": "postgres"
    },
    "mcp-installer": {
      "command": "npx",
      "args": [
        "@anaisbetts/mcp-installer"
      ]
    }
  }
}

[andrefelipe18]

Same error here, any resolution @daBee ?

[daBee]

Nothing yet.

[AgentSmithers]

I am receiving this while building a STDIO to SSE bridge. Judging by the response time I don't think the webserver can response fast enough before this error is sent by the Claude client. Can one receiving this error confirm that their MCP server is sending a response before receiving this within the log?

[daBee]

I've just asked the Claude client to reinstall the postgresql mcp server and I now have three of them in there. It's more confusing now than before. I now have mcp-postgresql, mcp=potgres, and postgresql MCP servers reporting "Could not attach to MCP Server ". It asked me to restart the app because of a fresh install twice, after I inserted my credentials for the first version, which I had to install twice, and now all of those are gone, and I have entries for the three I just mentioned, none with any credentials in the JSON.

[AgentSmithers]

So funny enough I just resolved my own bug. It turns out the bridge I was using was forwarding a blank response from the SSE server because the SSE server is required to send 202 Accepted (no body). The STDIO bridge would receive this and forward the blank message back to Claude Desktop as a response to the "initialize" method being invoked and Claude seems to be trying to parse that blank message as a JSON. I was at first thinking it was a timing issue initially.

In my project I simply added
'''
if (payload.Length > 0)
{
Console.WriteLine(payload); //<-- Forward message from SSE back to STDIO
LogMessage("Server->Client", $"[data: {payload}]");
}
else
{
LogMessage("Server->X", $"[Data is blank]");
}
'''

And it resolved the issue. Now it appears I have a working Console STIDO -> SSE bridge in c#.

Note: I hope my comments are on topic, I am not attempting to POST hijack. :)

[olaservo]

Hi @daBee I know its been ages since you opened this, but if you're still trying to resolve this I'm curious if you found what cause for your error was. I was having similar issues when my database wasn't running when I thought it was, so if you're still looking to fix this, then it could help to share more details on how your database is set up.

In general I think this server could use more useful error or debug logs since the connection closed error is very generic.

[daBee]

It's a LAN postgresql database. Nothing fancy. I have completely lost all bearing on what I should be using with postgresql.

[Priyanka06-droid]

I am seeing the same error when trying to integrate with aws athena mcp server with cursor.
STREAM 47931: push <Buffer 0a>
[MCP Error] SyntaxError: Unexpected end of JSON input
at JSON.parse ()
at deserializeMessage (file:///opt/homebrew/lib/node_modules/@lishenxydlgzs/aws-athena-mcp/node_modules/@modelcontextprotocol/sdk/dist/esm/shared/stdio.js:26:44)
at ReadBuffer.readMessage (file:///opt/homebrew/lib/node_modules/@lishenxydlgzs/aws-athena-mcp/node_modules/@modelcontextprotocol/sdk/dist/esm/shared/stdio.js:19:16)
at StdioServerTransport.processReadBuffer (file:///opt/homebrew/lib/node_modules/@lishenxydlgzs/aws-athena-mcp/node_modules/@modelcontextprotocol/sdk/dist/esm/server/stdio.js:39:50)
at StdioServerTransport._ondata (file:///opt/homebrew/lib/node_modules/@lishenxydlgzs/aws-athena-mcp/node_modules/@modelcontextprotocol/sdk/dist/esm/server/stdio.js:17:18)
at ReadStream.emit (node:events:507:28)
at addChunk (node:internal/streams/readable:559:12)
at readableAddChunkPushByteMode (node:internal/streams/readable:510:3)
at Readable.push (node:internal/streams/readable:390:5)
at TTY.onStreamRead (node:internal/stream_base_commons:189:23)