What
MCP servers are outside programs that give Claude extra tools. Claude Code now refuses a configured MCP server whose address it reserves for its own use, and reports this as a third kind of MCP failure, next to connection failures and servers blocked by managed policy.
- The refusal reason is
reserved_address, with the message "MCP server refused by Claude Code, which reserves its address". - Claude is told that these servers are refused because Claude Code reserves their address, that retrying will not help, and that whoever added the entry can remove it or change its address.
- A tool from such a server tells Claude the tool is unavailable.
- ToolSearch gives the same note when it finds no match.
Before, failed servers were split only into policy-blocked servers and other connection failures.
Why
If one of your MCP entries clashes with an address Claude Code uses itself, you get an accurate explanation instead of a plain connection failure that Claude may keep retrying.