CLAUDE_AGENT_SDK_MCP_NO_PREFIX

Updated October 13, 2026 by Alex Sorokoletov

CLAUDE_AGENT_SDK_MCP_NO_PREFIX is a Claude Code environment variable: Don't prefix MCP tool names with server name. Present since v2.1.69 or earlier and still present in v2.1.294. It is listed in the official reference.

How to set it

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

export CLAUDE_AGENT_SDK_MCP_NO_PREFIX=<value>
claude

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

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

Release notes that mention it

• 83 Undocumented Claude Code Environment Variables (v2.1.19)

Related variables

• CLAUDE_AGENT_SDK_DISABLE_MCP_MANIFESTS
• CLAUDE_AGENT_SDK_CLIENT_APP: Client application name.
• CLAUDE_AGENT_SDK_DISABLE_BUILTIN_AGENTS: Disable built-in agent types.
• CLAUDE_AGENT_SDK_VERSION: Agent SDK version sent in User-Agent header.
• CLAUDE_AGENT: Short-form identifier for the current agent, used in inter-agent messaging and log attribution.
• CLAUDE_CODE_AGENT: Full agent descriptor passed into a spawned agent process — likely the agent's frontmatter (tools, allowed/disallowed lists, system prompt path) so the child can reconstruct its runtime without re-reading disk.
• CLAUDE_CODE_AGENT_COST_STEER: Controls cost-aware behavior for subagent delegation.
• CLAUDE_CODE_AGENT_LIST_IN_MESSAGES: An early agent-listing toggle, made obsolete by the Agent View and coordinator surfaces that now own how agents are shown.

Frequently asked questions

All variables, searchable: Claude Code environment variables.