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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 v2.1.219

"__proto__" rejected as an MCP server name

You'll notice
Useful3 Signal0
MCP

An MCP server literally named __proto__ now warns you instead of silently loading nothing.

mcpServers
What

An MCP config with a literal __proto__ key under mcpServers used to be swallowed by prototype semantics, loading nothing and saying nothing. It is now detected and reported.

Details
  • Surfaces as a validation warning with skipReason reserved_name, which feeds the new skipped-server reporting
  • Warning messages and suggestions are now passed through a sanitizer before being pushed
Evidence

"__proto__" is a reserved MCP server name and was not loaded

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

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.219 →