CLAUDE_AGENT_SDK_MCP_NO_PREFIX
A Claude Code environment variable, read out of the shipped bundle. It has been in the build since v2.1.138, including the newest one read.
What it is
Set to 1 to skip the mcp__<server>__ prefix on tool names from SDK-created MCP servers. Tools use their original names. SDK usage only
Anthropic's own wording. Read off Environment variables, captured 2026-08-28.
Presence across releases
| Releases | Reading | Declared type | Default |
|---|---|---|---|
| 2.1.245 – 2.1.250 5 releases | never mined | — | — |
| 2.1.160 – 2.1.243 75 releases | in the build | bool | — |
| 2.1.138 – 2.1.159 20 releases | in the build | — | — |
A row reading never mined is a release with no archived bundle behind it. Nothing was read out of it, so nothing here says whether the name was in it. A declared type or a default is only ever what that release's own bundle stated.
Changelog entries naming it
No changelog entry here has ever named it. That is a statement about what has been written, not about the name: it has been in the build since v2.1.138 without anybody writing a line about it.
Documentation pages
- Environment variables reference table Claude Code CLI
A reference table page is one whose own table defines this name, and it is where the description above came from. A page that mentions it carries the name somewhere in its text and may say nothing about it at all. Every page carrying it.
Names beside it
Every environment variable in the inventory starting claude_agent_sdk, up to twelve of them.
CLAUDE_AGENT_SDK_CLIENT_APPNo description from anybody. 2.1.138
CLAUDE_AGENT_SDK_DISABLE_BUILTIN_AGENTSSet to 1 to disable all built-in [subagent](/docs/en/sub-agents) types such as Explore and Plan. Only applies in non-interactive mode (the -p flag). Useful for SDK users who want a blank slate. This also removes general-purpose, the subagent Claude Code runs when an Agent tool call omits subagent_type. Such a call then fails with [subagent_type is required](/docs/en/errors#subagent-type-is-required) 2.1.138
CLAUDE_AGENT_SDK_VERSIONYour entrypoint and SDK version are checked against known values before being reported. 2.1.138
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the environment variable does. All environment variables.