# MCP Servers on Windows: npx.cmd, Paths and PowerShell Fixes

> Every Windows-only reason an MCP server won't start in Claude Desktop, Cursor or VS Code: npx.cmd and spawn EINVAL, backslashes in JSON, the Microsoft Store python stub, PowerShell's where alias and execution policy, Docker's named pipe, and environment variables that never arrive. Exact error text and the fix for each.

**Source:** https://mcpplaygroundonline.com/blog/mcp-server-windows-npx-not-working  
**Author:** Nikhil Tiwari  
**Published:** 2026-11-06  
**Category:** Troubleshooting  
**Reading time:** 10 min read  
**Topics:** mcp server windows npx not working, mcp server windows, claude desktop mcp windows, spawn npx ENOENT windows, spawn EINVAL npx.cmd, cmd /c npx mcp, mcp config windows path backslash, python was not found microsoft store mcp, npx.ps1 cannot be loaded because running scripts is disabled, claude_desktop_config.json windows location

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📖 TL;DR

-   **`npx` on Windows is `npx.cmd`, a batch file.** Use `"command": "cmd"` with `"/c", "npx"` at the start of `args`. Writing `npx.cmd` gives `spawn EINVAL`.
-   **Double every backslash in JSON paths** (`C:\\Users\\me`), or use forward slashes. One single backslash breaks the whole config file.
-   **`python` may be the Microsoft Store stub**, which prints "Python was not found" and exits. Point the config at a real Python or use `uv`.
-   **In PowerShell, `where` is not `where.exe`.** Use `where.exe npx` or `Get-Command npx` to find a program.
-   **Quit the client from the system tray** after installing Node, Python or uv, or after changing environment variables. Closing the window leaves the old PATH in memory.

## Table of Contents

-   [Error → cause → fix](#table)
-   [Where the config and logs are on Windows](#config-file)
-   [1\. npx: spawn ENOENT, spawn EINVAL and "not recognized"](#npx)
-   [2\. Backslashes in JSON paths](#json)
-   [3\. Paths with spaces in "command"](#spaces)
-   [4\. Python, uv and the Microsoft Store stub](#python)
-   [5\. Docker Desktop isn't running](#docker)
-   [6\. Environment variables that never arrive](#env)
-   [7\. PowerShell traps while you test](#powershell)
-   [8\. The client still has the old PATH](#restart)
-   [Test the server outside the client](#test)
-   [FAQ](#faq)

Most MCP setup guides are written on a Mac. Copy one of their configs to Windows and the server often doesn't start, with an error that doesn't say why. This post collects the Windows-only causes in one place. For the general version of the npx problem, see [fixing spawn npx ENOENT](/blog/fix-spawn-npx-enoent-mcp).

## Error → cause → fix

What you see

Cause

Fix

`spawn npx ENOENT`

`npx` is a `.cmd` file, not an `.exe`

[`cmd /c npx`](#npx)

`spawn EINVAL`

`"command": "npx.cmd"`; Node refuses `.cmd` files without a shell

[`cmd /c npx`](#npx)

`'npx' is not recognized as an internal or external command`

The `cmd /c` wrapper works, but Node isn't on the client's PATH

[Install Node, then quit the client from the tray](#restart)

All servers gone, or a JSON error

A single backslash in a path

[`\\` or `/`](#json)

`Python was not found; run without arguments to install from the Microsoft Store…`

The Store alias, not a real Python

[Real Python path, or `uv`](#python)

`…//./pipe/dockerDesktopLinuxEngine: The system cannot find the file specified.`

Docker Desktop isn't running

[Start Docker Desktop](#docker)

Server starts, then says a key or token is missing

The variable is set in Windows, not in the config

[Put it in `"env"`](#env)

## Where the config and logs are on Windows

-   **Claude Desktop config:** `%APPDATA%\Claude\claude_desktop_config.json`
-   **Claude Desktop logs:** `%APPDATA%\Claude\logs\`, with one `mcp-server-NAME.log` per server
-   **Cursor:** `%USERPROFILE%\.cursor\mcp.json`
-   **VS Code:** `%APPDATA%\Code\User\mcp.json`

To open a folder, press Win+R and paste the path, for example `%APPDATA%\Claude\logs`. The server's own error is almost always in its log file, so read that before you change anything.

## 1\. npx: spawn ENOENT, spawn EINVAL and "not recognized"

Node installs `npx` on Windows as `npx.cmd`, a batch script. MCP clients start servers with Node's `child_process.spawn` and no shell, which only runs real executables. So the client looks for `npx`, finds no `npx.exe`, and logs `spawn npx ENOENT`.

Writing `"command": "npx.cmd"` doesn't fix it. Since the April 2024 Node security releases (CVE-2024-27980), Node won't start `.cmd` or `.bat` files without a shell and throws `spawn EINVAL` instead.

The fix that works in every client is to let `cmd.exe` start `npx`:

```
{
  "mcpServers": {
    "filesystem": {
      "command": "cmd",
      "args": ["/c", "npx", "-y", "@modelcontextprotocol/server-filesystem", "C:\\Users\\me\\projects"]
    }
  }
}
```

The same goes for `pnpm dlx`, `yarn dlx` and `bunx` when they're installed as `.cmd` shims. `uvx` from the official uv installer is a real `uvx.exe`, so it doesn't need the wrapper.

**Once you add `cmd /c`, the error changes.** If Node isn't on the client's PATH, the spawn now succeeds (it started `cmd`), and the server log shows cmd's own message instead:

```
'npx' is not recognized as an internal or external command,
operable program or batch file.
```

That means the wrapper is right and Node is the problem. Check with `where.exe npx` in a new terminal, then see [section 8](#restart).

## 2\. Backslashes in JSON paths

In JSON, a backslash starts an escape sequence like `\n`. `\U` in `C:\Users` isn't a valid one, so the whole file fails to parse. Node's JSON parser, for example, reports this for `"C:\Users\me\projects"`:

```
Bad escaped character in JSON at position 13 (line 1 column 14)
```

Clients react differently. Some show an error, some just start with **no servers at all**, because they couldn't read any of the file. Two ways to write the path:

```
"C:\\Users\\me\\projects"   // doubled backslashes
"C:/Users/me/projects"       // forward slashes, which Windows accepts too
```

JSON doesn't allow comments, so leave the `//` notes above out of your real file. Paste the file into any JSON validator before restarting the client.

## 3\. Paths with spaces in "command"

If you point `command` at a full path, **don't add quotes inside the string**. Without a shell, nothing removes them, and Windows looks for a file whose name starts with a quote mark:

```
"command": "\"C:\\Program Files\\nodejs\\node.exe\""   // fails: ENOENT
"command": "C:\\Program Files\\nodejs\\node.exe"         // works
```

The same applies to items in `args`: each array item is passed as one argument, spaces included, so it needs no extra quotes.

## 4\. Python, uv and the Microsoft Store stub

A fresh Windows install has a `python.exe` on PATH that isn't Python. It's an "app execution alias" that opens the Microsoft Store. When an MCP client starts it, it prints this to stderr and exits:

```
Python was not found; run without arguments to install from the Microsoft Store, or disable this shortcut from Settings > Manage App Execution Aliases.
```

The client usually shows only that the server closed or disconnected, so look for this line in the server's log. Three fixes, best first:

1.  **Use uv**, which manages its own Python: `winget install astral-sh.uv`, then `"command": "uvx"` for published servers or `"command": "uv"` with `run --directory C:/path/to/project server.py` for your own. My [uv tutorial](/blog/test-python-mcp-server-locally-uv) walks through it.
2.  **Point at the project's virtual environment:** `"command": "C:/path/to/project/.venv/Scripts/python.exe"`. Note `Scripts`, not `bin` as on Mac and Linux.
3.  **Install Python from python.org** with "Add python.exe to PATH" ticked, and turn off the `python.exe` and `python3.exe` aliases under Settings → Apps → Advanced app settings → App execution aliases.

## 5\. Docker Desktop isn't running

Servers started with `"command": "docker"` need the Docker engine. If Docker Desktop is installed but not running, `docker` starts fine and then fails. The message ends like this:

```
error during connect: ... open //./pipe/dockerDesktopLinuxEngine: The system cannot find the file specified.
```

Start Docker Desktop, wait until it says the engine is running, then restart the client. If you want it to always be ready, turn on "Start Docker Desktop when you sign in" in Docker's settings.

## 6\. Environment variables that never arrive

You set `GITHUB_TOKEN` with `setx` or in System Properties, it shows up in a new terminal, but the server still says it's missing.

Two separate causes:

-   **The client was already running.** A Windows program gets its environment when it starts. Quit it from the tray and open it again.
-   **The client doesn't pass it on.** Clients built on the official MCP TypeScript SDK's stdio transport give the server only a short list of system variables by default: `APPDATA`, `PATH`, `PATHEXT`, `TEMP`, `USERPROFILE`, `SYSTEMROOT` and a few more. Everything else, your token included, has to be in the server's `"env"`.

```
"github": {
  "command": "cmd",
  "args": ["/c", "npx", "-y", "@modelcontextprotocol/server-github"],
  "env": { "GITHUB_PERSONAL_ACCESS_TOKEN": "ghp_..." }
}
```

The same applies to proxy settings: if you're behind a corporate proxy, put `HTTPS_PROXY` in `"env"` too, or `npx` can't download the package.

## 7\. PowerShell traps while you test

Testing in a terminal is the right instinct. PowerShell adds two problems of its own.

### "where npx" prints nothing

In PowerShell, `where` is an alias for `Where-Object`, not the Windows `where.exe` program. `where npx` runs a filter on empty input and prints nothing, which looks like "npx isn't installed". Use one of these instead:

```
where.exe npx
Get-Command npx
```

`where npx` works as expected in `cmd.exe`.

### npx.ps1 cannot be loaded

Node also installs `npx.ps1`, and PowerShell prefers it to `npx.cmd`. With the default execution policy on Windows clients, running it fails:

```
npx : File C:\Program Files\nodejs\npx.ps1 cannot be loaded because running scripts is disabled on this system. For more information, see about_Execution_Policies at https:/go.microsoft.com/fwlink/?LinkID=135170.
```

This only affects your terminal, not MCP clients, which don't start servers through PowerShell. Either type `npx.cmd` in PowerShell, test in `cmd.exe`, or allow local scripts for your user:

```
Set-ExecutionPolicy -Scope CurrentUser RemoteSigned
```

## 8\. The client still has the old PATH

Installers for Node, Python and uv add their folder to PATH, but only programs started afterwards see the change. Claude Desktop keeps running in the system tray when you close its window, so it can hold the old PATH for days.

1.  Open a **new** terminal and run `where.exe npx` (or `uvx`, `python`, `docker`). If it finds nothing, the program isn't on PATH yet: reinstall it with the PATH option ticked.
2.  If it's found, quit the client completely: right-click its tray icon and choose Quit. For Cursor and VS Code, close every window.
3.  Open the client again.

With nvm-windows, also run `nvm use` with a version once, so the `nodejs` folder it puts on PATH actually points somewhere.

## Test the server outside the client

Before you restart the client again, run the exact command from your config in `cmd.exe`:

```
cmd /c npx -y @modelcontextprotocol/server-filesystem C:\Users\me\projects
```

A working stdio server prints nothing, or a line to stderr, and then waits for input. That's correct: it's waiting for JSON-RPC. Press Ctrl+C to stop it. If it exits with an error instead, you've found the real problem. For servers that work here but not in the client, see [MCP server works in the terminal but not in Claude Desktop](/blog/mcp-server-works-in-terminal-not-claude-desktop).

To go further and call tools, [MCP Playground Desktop](/local-mcp-server-testing) runs on Windows and starts stdio servers the way a client does:

-   **Plain `npx` works.** It starts `.cmd` scripts correctly, so you can check the server itself before getting the `cmd /c` wrapper right. Configs that already use `cmd /c` work too.
-   **Import** reads `%APPDATA%\Claude\claude_desktop_config.json`, Cursor's and VS Code's files, so you [don't retype anything](/blog/import-claude-desktop-cursor-mcp-config).
-   **Missing programs get a clear message**: "Couldn't find "uvx" on this computer." with the `winget install astral-sh.uv` command, instead of `spawn uvx ENOENT`.
-   **The Server stderr tab** shows what the server printed, including the "Python was not found" line from the Store stub.

## FAQ

**Why does npx not work in my MCP config on Windows?+**

On Windows npx is npx.cmd, a batch file, and MCP clients start servers without a shell, so they can't run it. Set command to cmd and start args with /c and npx, followed by the package and its arguments.

**What does spawn EINVAL mean for an MCP server?+**

The command is a .cmd or .bat file, such as npx.cmd. Since April 2024 Node refuses to start those without a shell. Use cmd with /c in args instead of calling the .cmd file directly.

**How do I write Windows paths in claude_desktop_config.json?+**

Double every backslash, as in C:\\\\Users\\\\me\\\\projects, or use forward slashes, as in C:/Users/me/projects. A single backslash makes the whole file invalid JSON.

**Where is claude_desktop_config.json on Windows?+**

In %APPDATA%\\Claude\\claude\_desktop\_config.json. The logs are in %APPDATA%\\Claude\\logs, with one file per MCP server.

**Why does my Python MCP server say "Python was not found" on Windows?+**

The python on PATH is the Microsoft Store app execution alias, not a real Python. Use uv, point the config at your virtual environment's .venv\\Scripts\\python.exe, or install Python from python.org and turn the aliases off in Settings.

**Why does "where npx" show nothing in PowerShell?+**

In PowerShell, where is an alias for Where-Object. Run where.exe npx or Get-Command npx instead, or use where npx in cmd.exe.

## Conclusion

On Windows, most MCP servers that won't start fall into one of these causes: `npx` without `cmd /c`, a single backslash, the Store python stub, Docker not running, a variable missing from `"env"`, or a client that still has the old PATH. **Read the server's log in `%APPDATA%\Claude\logs` first**, then fix the one it points to.

To check a server works before you touch the client config again, [get MCP Playground Desktop for Windows and Mac →](/local-mcp-server-testing)

## Frequently asked questions

### Why does npx not work in my MCP config on Windows?

On Windows npx is npx.cmd, a batch file, and MCP clients start servers without a shell, so they can't run it. Set command to cmd and start args with /c and npx, followed by the package and its arguments.

### What does spawn EINVAL mean for an MCP server?

The command is a .cmd or .bat file, such as npx.cmd. Since April 2024 Node refuses to start those without a shell. Use cmd with /c in args instead of calling the .cmd file directly.

### How do I write Windows paths in claude_desktop_config.json?

Double every backslash, as in C:\\Users\\me\\projects, or use forward slashes, as in C:/Users/me/projects. A single backslash makes the whole file invalid JSON.

### Where is claude_desktop_config.json on Windows?

In %APPDATA%\Claude\claude_desktop_config.json. The logs are in %APPDATA%\Claude\logs, with one file per MCP server.

### Why does my Python MCP server say "Python was not found" on Windows?

The python on PATH is the Microsoft Store app execution alias, not a real Python. Use uv, point the config at your virtual environment's .venv\Scripts\python.exe, or install Python from python.org and turn the aliases off in Settings.

### Why does "where npx" show nothing in PowerShell?

In PowerShell, where is an alias for Where-Object. Run where.exe npx or Get-Command npx instead, or use where npx in cmd.exe.


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_Canonical page: https://mcpplaygroundonline.com/blog/mcp-server-windows-npx-not-working — MCP Playground (mcpplaygroundonline.com), the free browser-based tool for testing MCP servers and building AI agents._