[BUG] MCP Fails on native Windows

Status Fixed / completed

Maintainer reply ✓ Yes — ollie-anthropic

Activity 9 comments · opened Jul 12, 2025 · closed Jul 18, 2025

💡 Likely answer: A maintainer (ollie-anthropic, collaborator) responded on this thread — see the highlighted reply below.

Environment

Platform (select one): Claude Max Sub
Claude CLI version: 1.0.51
Operating System: Windows 11
Terminal: Powershell

Bug Description

The MCP functionality is not working on Windows (native installation). When attempting to add a stdio MCP.

Steps to Reproduce

Open a terminal (e.g., PowerShell, Cmd).
Attempt to add a context using the claude mcp add command, for example:

claude mcp add context7 -- "npx -y @upstash/context7-mcp"

Expected Behavior

The MCP should be successfully added - It's working on WSL2 on the same machine.

Actual Behavior

The MCP command fails with the following error log, indicating a "Connection closed" issue:

{
  "debug": "Error stack: McpError: MCP error -32000: Connection closed\n    at ka1._onclose (file:///C:/Users/FooBar/AppData/Roaming/npm/node_modules/@anthropic-ai/claude-code/cli.js:1336:15216)\n    at _transport.onclose (file:///C:/Users/FooBar/AppData/Roaming/npm/node_modules/@anthropic-ai/claude-code/cli.js:1336:14535)\n    at ChildProcess.<anonymous> (file:///C:/Users/FooBar/AppData/Roaming/npm/node_modules/@anthropic-ai/claude-code/cli.js:1338:1459)\n    at ChildProcess.emit (node:events:518:28)\n    at ChildProcess.emit (node:domain:489:12)\n    at LbQ.A.emit (file:///C:/Users/FooBar/AppData/Roaming/npm/node_modules/@anthropic-ai/claude-code/cli.js:320:155823)\n    at maybeClose (node:internal/child_process:1104:16)\n    at Socket.<anonymous> (node:internal/child_process:456:11)\n    at Socket.emit (node:events:518:28)\n    at Socket.emit (node:domain:489:12)",
  "timestamp": "2025-07-11T23:43:11.730Z",
  "sessionId": "8c2cb375-4da4-48e2-9d0f-f37c8f0ccae7",
  "cwd": "D:\\FooBar\\bpress"
}

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9 Comments

Vanyangyang · 1 year ago

@vuhoanglam Try this，Using cmd /c wrapper The most reliable solution is to use cmd /c to ensure npx is executed in the correct shell environment
：

json
{
"mcpServers": {
"context7": {
"command": "cmd",
"args": ["/c", "npx", "-y", "@upstash/context7-mcp@latest"]
}
}
}

GJayLG · 1 year ago

same

ismailhozza · 1 year ago

Same issue. Where does claude code store mcp config json?

GiampaoloGabba · 1 year ago

@vuhoanglam Try this，Using cmd /c wrapper The most reliable solution is to use cmd /c to ensure npx is executed in the correct shell environment ： json { "mcpServers": { "context7": { "command": "cmd", "args": ["/c", "npx", "-y", "@upstash/context7-mcp@latest"] } } }

i can confirm that this works pretty well

vuhoanglam · 1 year ago

Nice. U guys can try @Vanyangyang method, use mcp add-json instead of add:

claude mcp add-json context7 -s user '{"type":"stdio","command":"cmd","args": ["/c", "npx", "-y", "@upstash/context7-mcp@latest"]}'

document link: https://docs.anthropic.com/en/docs/claude-code/mcp#add-mcp-servers-from-json-configuration

but i think the offiial document needs to be updated for windows users before marking this issue as resolved

dmastag · 1 year ago

Thanks for all the Input, to summary

Where does claude store the mcp config.json? (as per @ismailhozza)
It is stored in

C:\Users\[username]\.claude.json

There should be multiple mcpServers entries.
You should be able to recognize which ones are on a Project scope and which one are on a User Scope (Higher)

I just put this in and it started working

"mcpServers": {
    "context7": {
      "command": "cmd",
      "args": [
        "/c",
        "npx",
        "-y",
        "@upstash/context7-mcp@latest"
      ]
    },
    "browser-tools": {
      "command": "cmd",
      "args": [
        "/c",
        "npx",
        "-y",
        "@agentdeskai/browser-tools-mcp@1.2.0"
      ]
    },
    "browsermcp": {
      "command": "cmd",
      "args": [
        "/c",
        "npx",
        "-y",
        "@browsermcp/mcp@latest"
      ]
    }
  },

Now if you want to use a command line from terminal you can do like this:

Command Prompt:

claude mcp add-json browser-tools -s user "{\"command\":\"cmd\",\"args\":[\"/c\",\"npx\",\"-y\",\"@agentdeskai/browser-tools-mcp@1.2.0\"]}"

Powershell

claude mcp add-json browser-tools -s user '{\"command\":\"cmd\",\"args\":[\"/c\",\"npx\",\"-y\",\"@agentdeskai/browser-tools-mcp@1.2.0\"]}'

Hope this helps

Kudos to @Vanyangyang and @vuhoanglam

fengyang86 · 1 year ago

> @vuhoanglam Try this，Using cmd /c wrapper The most reliable solution is to use cmd /c to ensure npx is executed in the correct shell environment ： > json { "mcpServers": { "context7": { "command": "cmd", "args": ["/c", "npx", "-y", "@upstash/context7-mcp@latest"] } } } i can confirm that this works pretty well

it's good

ollie-anthropic collaborator · 1 year ago

Hey all, thanks a lot for the feedback on this. The solutions here involving using the cmd command seem to fix this. I've added some documentation on our website addressing this https://docs.anthropic.com/en/docs/claude-code/mcp. In the coming release, we'll also have a custom warning for Windows users, prompting them about a potentially misconfigured setup in this case.

I'll close the issue given a solution has been found. However, we do hope to make all this much more ergonomic!

github-actions[bot] · 1 year ago

This issue has been automatically locked since it was closed and has not had any activity for 7 days. If you're experiencing a similar issue, please file a new issue and reference this one if it's relevant.