What
Claude Code now validates MCP tool names against the emerging MCP naming standard and warns about non-conforming names.
Details
- Hard failures (tool rejected): empty names, names exceeding 128 characters, names with characters outside
[A-Za-z0-9._-] - Soft warnings (tool registered but warning logged): names with spaces, commas, leading/trailing dashes or dots
- Warning output references the MCP specification proposal: [SEP: Specify Format for Tool Names](https://github.com/modelcontextprotocol/modelcontextprotocol/issues/986)
- Registration proceeds for soft warnings: "Tool registration will proceed, but this may cause compatibility issues."
Evidence
Tool name validation (search for "Tool name validation warning", "Tool name contains invalid characters", "Allowed characters are")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.