CLAUDE_CODE_MCP_SERVE_TUNNEL_BINARY_FRAMES

Updated November 9, 2026 by Alex Sorokoletov

CLAUDE_CODE_MCP_SERVE_TUNNEL_BINARY_FRAMES is a Claude Code environment variable. Added in v2.1.318 and still present in v2.1.321. It is not in the official reference.

How to set it

For one session, export it in the shell that starts Claude Code:

export CLAUDE_CODE_MCP_SERVE_TUNNEL_BINARY_FRAMES=<value>
claude

To apply it to every session, add it to the env object of a settings file:

// ~/.claude/settings.json
{
  "env": {
    "CLAUDE_CODE_MCP_SERVE_TUNNEL_BINARY_FRAMES": "<value>"
  }
}

Related variables

• CLAUDE_CODE_MCP_SERVE_ENABLED_PLUGINS: Lists the plugins to enable for the MCP serve process as JSON; the named plugins are merged into the enabled-plugins config and switched on.
• CLAUDE_CODE_MCP_SERVE_GARBAGE_COLLECTIONS: Controls garbage collection while serving MCP; when enabled the serve process runs full or young (eden) collections; the default comes from a server-side setting.
• CLAUDE_CODE_MCP_SERVE_INTERFACE_MIN_VERSION: Sets the minimum tool-host interface version advertised when serving MCP; a value that differs from what the running daemon reports is ignored and logged.
• CLAUDE_CODE_MCP_SERVE_SETTINGS: Provides JSON permission settings for the MCP serve process, parsed into allow and deny rule lists that scope what the server may do.
• CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT: When true, enables the experimental MCP serve tool-output path, which validates and attaches tool deny rules; off otherwise.
• CLAUDE_CODE_MCP_SERVE_WORKSPACE_ROOT: Used by claude mcp serve --transport http.
• CLAUDE_CODE_ARTIFACT_MCP: Enables MCP runtime-capability support for artifacts; on by default.
• CLAUDE_CODE_CHROME_LATE_MCP_SERVER: When true, loads the alternate late Claude-in-Chrome MCP server module and skips installing the Chrome native host early.

Frequently asked questions

All variables, searchable: Claude Code environment variables.