CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT

Updated October 14, 2026 by Alex Sorokoletov

CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT is a Claude Code environment variable. Added in v2.1.287 and still present in v2.1.295. It is not in the official reference.

Status	Present in v2.1.295
Added	Added in v2.1.287
Category	MCP
Official docs	Not listed

How to set it

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

export CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT=<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_TOOL_OUTPUT": "<value>"
  }
}

Related variables

ENABLE_MCP_LARGE_OUTPUT_FILES: Enable large output files for MCP.
CLAUDE_CODE_MCP_SERVE_SETTINGS
CLAUDE_CODE_ENABLE_REFRESH_MCP_TOOLS: Enables an on-demand MCP-tool refresh capability, grouped with CLAUDE_CODE_ENABLE_TASKS and CLAUDE_CODE_ENABLE_REMOTE_RECAP.
CLAUDE_CODE_MAX_MCP_DESCRIPTION_LENGTH
CLAUDE_CODE_MCP_ALLOWLIST_ENV: Specifies an allowlist of environment variables that MCP servers can access.
CLAUDE_CODE_MCP_AUTO_BACKGROUND_MS
CLAUDE_CODE_MCP_INSTR_DELTA: Delta/incremental MCP instruction updates.
CLAUDE_CODE_MCP_SERVER_NAME: Added in v2.1.85 to identify which MCP server a helper process was acting on behalf of.

Frequently asked questions

Which Claude Code version has CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT?

Added in v2.1.287 and still present in v2.1.295.

How do I set CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT?

Export it before starting Claude Code (export CLAUDE_CODE_MCP_SERVE_TOOL_OUTPUT=value), or add it to the "env" object in ~/.claude/settings.json to apply it to every session.

All variables, searchable: Claude Code environment variables.