[Bug]: CLI bootstrap leaks initialization diagnostic logs to stdout on Windows

[AsifpMulla123]

Chrome version

N/A (CLI / MCP protocol backend issue)

Extension version

@nhonh/react-debugger@latest

React version

N/A (CLI issue)

Page URL

N/A (CLI issue)

Steps to reproduce

1. Install an MCP client (such as the Cline VS Code extension) on a Windows environment.
2. Add the React Debugger MCP configuration block using npx @nhonh/react-debugger@latest mcp as the command server arguments.
3. Attempt to initialize or launch the server connection from the host client.
4. Observe the connection dropping immediately with strict JSON parsing stream crashes.

Expected behavior

The MCP server should communicate strictly using pure JSON-RPC over the standard stdout channel. Any human-readable diagnostic messages, installer telemetry text, or bootstrap logging should be isolated completely to stderr so it does not corrupt the strict client-side JSON input stream parser.

Actual behavior

The CLI bootstrap layer leaks raw installation and initialization diagnostic text logs directly into the stdout pipe on Windows environments. This passes raw, unformatted text strings to the client stream listener, triggering JSON parser exceptions and abruptly dropping the connection. ### Environment Info

• OS: Windows
• Node.js Version: v22.18.0

Console errors

Unexpected token 'R', " React Debu"... is not valid JSON
Unexpected token 'R', "Running in"... is not valid JSON
Unexpected token 'I', "Installing"... is not valid JSON
Unexpected token 'D', "Downloadin"... is not valid JSON
Unexpected token 'D', "Download complete!" is not valid JSON
Unexpected token '✓', "✓ Installa"... is not valid JSON
MCP error -32000: Connection closed

Screenshot of the extension panel

No response

Pre-submission checklist

• I searched existing issues and did not find a duplicate
• I am running the latest version of the extension
• I read SUPPORT.md and this is a bug, not a usage question

[hoainho]

Hi @AsifpMulla123 — thank you for the high-quality bug report! Reproduction steps + console errors + environment info all in one issue is exactly what we need.

You're 100% right — the MCP JSON-RPC contract requires stdout to be pure JSON only. Any console.log() in the bootstrap path will corrupt the stream on the client side. This is a real bug that affects all MCP clients (Cline, Claude Desktop, opencode), not just Windows — Windows is just where it bites first because of the slower stdout buffering.

Root cause hypothesis (to confirm)

Looking at cli/src/cli.ts and cli/src/mcp/server.ts, the likely culprits are:

1. Installer telemetry — anything that writes Installing, Running in, React Debugger v... to stdout during npx bootstrap
2. logger.info() calls going to stdout instead of stderr
3. process.stdout.write() anywhere outside the MCP message serializer
4. npm/npx itself sometimes writes progress to stdout when running with old Node versions (though v22.18.0 should be clean)

Triage labels

Bumping priority to bug + mcp + good first issue since the fix is mechanical (audit all console.log / process.stdout.write calls in cli/src/ and route to stderr instead). I'll label it needs-fix once I do a quick audit pass myself.

Workaround for now

For anyone hitting this before the fix lands:

# Wrap the command to redirect stderr away (NOT stdout)
npx @nhonh/react-debugger@latest mcp 2>/dev/null

⚠️ But this only works on Unix shells — not native Windows cmd. The proper fix is what you described.

Are you interested in fixing it?

Given your excellent diagnosis, you have the clearest mental model already. If you'd like to take the PR (would be a fast one — grep -rn 'console.log\|process.stdout' cli/src/ + replace with console.error() / process.stderr.write()), drop I'll take this here and the issue is yours.

If not — totally fine, this becomes a good first issue for the next contributor. Either way thanks for the careful report. 🙏

[AsifpMulla123]

I'll take this! Thanks for the root-cause guidance. I'll audit the cli/src/ directory for any stray console.log or process.stdout references and pivot them to stderr or console.error. Expect a PR shortly!

[AsifpMulla123]

PR is officially open for review here: #49

Tested locally, confirmed that stdout remains at 0 bytes while running non-interactively, and included the console log capture in the description. Thanks again for the quick triage!