[BUG] MCP server 'args' configuration ignored - servers launched without specified arguments

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code ignores the args field in MCP server configuration (~/.claude.json), launching MCP servers without passing the specified command-line arguments. This prevents proper configuration of MCP servers that require arguments to function correctly.

What Should Happen?

Claude Code should pass all arguments specified in the args array of an MCP server configuration to the server process when launching it, similar to how other MCP-compatible tools (like codex) handle the same configuration.

Error Messages/Logs

No error messages - the server launches but silently ignores configured arguments.

Steps to Reproduce

Install Brave Browser on Mac

Configure an MCP server with arguments in ~/.claude.json:

{
  "mcpServers": {
      "playwright": {
          "command": "/opt/homebrew/bin/npx",
          "args": [
            "@playwright/mcp@latest",
            "--extension",
            "--executable-path=/Applications/Brave Browser.app/Contents/MacOS/Brave Browser"
          ]
      }
  }
}

Start Claude Code: _claude --debug_

Check the running process: _ps aux | grep mcp-server-playwright_

Actual result: Process runs without arguments:

node /Users/alex/.npm/_npx/9833c18b2d85bc59/node_modules/.bin/mcp-server-playwright

Expected result: Process should run with configured arguments:

node /Users/alex/.npm/_npx/9833c18b2d85bc59/node_modules/.bin/mcp-server-playwright --extension --executable-path=/Applications/Brave Browser.app/Contents/MacOS/Brave Browser

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

1.0.120 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

The same MCP configuration works correctly in codex and other MCP-compatible agents.

Debug logs show MCP server connecting successfully but don't show the command/args being used

This affects any MCP server that requires command-line arguments