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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.251

Reserved MCP server names on hosted sessions must point at a loopback listener

You'll notice
Useful2 Signal3
MCP not in their notes

On hosted sessions, reserved MCP server names must point at a loopback listener.

CLAUDE_CODE_REMOTE
What

On hosted sessions, where CLAUDE_CODE_REMOTE is set, an MCP server added at runtime whose name matches a reserved set is refused unless it is an http server on a loopback IP address such as http://127.0.0.1:PORT/mcp. The refusal tells you to point it at the in-container listener or rename the server.

Details
  • Only reached for dynamically loaded server configs on hosted or remote sessions; local sessions are unaffected.
  • The address must be a literal loopback IP, not a hostname.
  • Which names are reserved is decided by an internal list that this build does not spell out.
Evidence

is reserved except as an http server on a loopback IP literal (e.g. http://127.0.0.1:PORT/mcp) and was not loaded, on a hosted session is reserved except as an http server on a loopback IP literal (e.g. http://127.0.0.1:PORT/mcp) and was not loaded

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.251 →