{"version":"2.1.287","anchor":"mcp-serve-tool-output-env-var-added-to-the-scrubbedforwarde","canonical_anchor":"mcp-serve-tool-output-env-var-added-to-the-scrubbedforwarde","heading":"New environment variable for tool output when Claude Code runs as an MCP server","tier":"use","area":"MCP","url":"https:\/\/changelogs.core-directive.com\/v\/2.1.287\/e\/mcp-serve-tool-output-env-var-added-to-the-scrubbedforwarde","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.287","markdown":"### New environment variable for tool output when Claude Code runs as an MCP server\n\nA new environment variable, `CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT`, appears alongside the other MCP server-mode variables\n\n**Unclear.** What this variable does, and whether the list it joins hides it from programs Claude Code starts, is not known.\n\n**What**\n\nClaude Code can run as an MCP server, meaning other programs connect to it using the Model Context Protocol and use its tools. A new environment variable, `CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT`, has been added to the same internal list as `CLAUDE_CODE_MCP_SERVE_AUTH_TOKEN` and `CLAUDE_CODE_MCP_SERVE_SETTINGS`. An environment variable is a named value set in your shell before a program starts.\n\n**Why**\n\nThe name suggests a new control over tool output in MCP server mode. It sits in a list of sensitive or internal variables, so it is probably not meant for everyday use.\n\n- Area: MCP\n- Tier: Use it now\n- Useful: 5\/5\n- Signal: 4\/5"}