fix: Use cmd /c wrapper for npx on Windows

[wonderwhy-er]

User description

Problem

On Windows, using npx.cmd or just npx directly in MCP server configurations has been failing with errors like:

• Cannot read properties of undefined (reading 'cmd')
• Connection failures when Claude Desktop tries to start the server

Root Cause

Windows requires a cmd /c wrapper to properly execute npx commands because:

• Node.js has difficulties spawning batch files like npx.cmd without setting the shell option
• npx is a script, not a traditional binary executable
• This is the officially recommended approach by Anthropic

Solution

Updated setup-claude-server.js to use the cmd /c wrapper pattern for Windows npx installations:

Before:

{
  "command": "npx.cmd",
  "args": ["@wonderwhy-er/desktop-commander"]
}

After:

{
  "command": "cmd",
  "args": ["/c", "npx", "-y", "@wonderwhy-er/desktop-commander"]
}

Changes

• ✅ Updated debug npx configuration to use cmd /c wrapper
• ✅ Updated standard npx configuration to use cmd /c wrapper
• ✅ Added -y flag to auto-accept npx prompts in standard mode
• ✅ Maintains compatibility with macOS/Linux (unchanged)

References

• Anthropic MCP Windows Documentation
• GitHub Issue: Windows npx wrapper requirement
• Example from Smithery MCP servers using this pattern

Testing

Tested on Windows 11 with:

• Claude Desktop latest version
• Node.js v22.17.1
• Both npx and local installation modes

---

CodeAnt-AI Description

Wrap Windows npx server launches with cmd /c

What Changed

• Windows debug mode now starts via cmd /c npx --inspect-brk=9229 so the debugger-targeted process launches instead of failing to spawn npx directly
• Windows standard mode now runs cmd /c npx -y, aligning with the existing Linux/macOS flow and preventing npx from hanging on prompts

Impact

✅ Fewer Windows startup failures
✅ Reliable debugger attachment on Windows
✅ No manual prompts when launching npx on Windows

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Summary by CodeRabbit

• Bug Fixes

  • Improved Windows handling for starting the server, ensuring debug/instrumentation flags work reliably.
  • Uniform application of environment settings across platforms.

• Refactor

  • Standardized invocation paths so installation/start commands behave consistently on Windows and non-Windows.
  • Added automatic confirmation for command-line installs and clarified debug vs. normal start flows.

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[coderabbitai]

Walkthrough

Refactors platform-specific npx execution in setup-claude-server.js, implementing cmd /c wrapper for Windows and direct npx invocation for non-Windows, while adding --inspect-brk=9229 flag for debug mode and -y flag for auto-confirmed installation across both platforms.

Changes

Cohort / File(s)	Summary
Cross-platform npx execution refactor setup-claude-server.js	Replaces platform-specific command construction with explicit Windows (cmd /c wrapper) and non-Windows (direct npx) code paths; adds --inspect-brk=9229 for debug mode and -y flag for package auto-confirmation in both standard and debug modes

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

• Verify Windows cmd /c wrapper syntax and argument ordering
• Confirm debug mode --inspect-brk flag placement and port value (9229)
• Check -y flag behavior for package auto-confirmation on both platforms
• Test cross-platform compatibility paths

Possibly related PRs

• DesktopCommanderMCP#93: Modifies the same file with overlapping changes to server configuration and npx launch logic in debug and standard modes.

Suggested labels

size:S

Suggested reviewers

• serg33v

Poem

🐰 A rabbit hops through Windows and Unix with glee,
cmd /c and npx dancing in harmony,
With --inspect-brk to debug the way,
And -y flags confirming, hip-hip-hooray!
Cross-platform paths aligned at last,
The server setup's running fast! ✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change—fixing Windows npx execution via cmd /c wrapper, which is the primary objective and code modification in the PR.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/windows-npx-cmd-wrapper

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CodeAnt AI finished reviewing your PR.

[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

setup-claude-server.js (1)

766-788: Consider adding the -y flag in debug mode for consistency.

The standard mode includes -y to auto-accept npx installation prompts (line 822, 830), but debug mode omits it. While developers in debug mode may want more control, unexpected prompts could interrupt the debugging workflow.

Consider adding -y to debug mode as well for a smoother experience:

                     if (isWindows) {
                         serverConfig = {
                             "command": "cmd",
                             "args": [
                                 "/c",
                                 "npx",
+                                "-y",
                                 "--inspect-brk=9229",
                                 packageSpec
                             ],
                             "env": debugEnv
                         };
                     } else {
                         serverConfig = {
                             "command": "npx",
                             "args": [
+                                "-y",
                                 "--inspect-brk=9229",
                                 packageSpec
                             ],
                             "env": debugEnv
                         };
                     }

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between c4fc187 and bf14fd4.

📒 Files selected for processing (1)

• setup-claude-server.js (2 hunks)

🧰 Additional context used

🧬 Code graph analysis (1)

setup-claude-server.js (1)

uninstall-claude-server.js (1)

• isWindows (367-367)

🔇 Additional comments (2)

setup-claude-server.js (2)

766-788: Windows wrapper implementation looks correct.

The cmd /c wrapper for npx on Windows is the correct solution to handle npx.cmd batch file execution issues. The platform-specific branching is clear and follows the recommended pattern from Anthropic documentation.

---

814-834: LGTM! Standard mode configuration is well-implemented.

The Windows cmd /c wrapper and -y flag additions correctly address the PR objectives:

• Fixes Windows npx execution failures with the cmd wrapper
• Prevents installation prompts with the -y flag
• Maintains clean separation between Windows and non-Windows paths

[wonderwhy-er]

Additional Fix Applied

Fixed the debug inspector flag handling based on code review:

Problem: The --inspect-brk=9229 flag was being passed as an npx argument, which doesn't work.

Solution: Moved the inspector flag to NODE_OPTIONS environment variable:

\\javascript
const debugEnv = {
'NODE_OPTIONS': '--inspect-brk=9229 --trace-warnings --trace-exit',
'DEBUG': '*'
};
\\

Now the flag is properly passed to Node.js instead of npx, allowing the debugger to attach correctly.

Commit: 8f05cd4