What
MCP (Model Context Protocol) is how Claude Code connects to outside tools and services. When the connection to an MCP server closes during a tool call, Claude Code is now more careful about sending the call again:
- Any call that is still in progress is not resent, not only one the server had already accepted.
- A call whose request went out but got no answer is not resent either.
In both cases the call fails with an error saying the server could not be reached, instead of retrying. Messages include Tool '${n}' failed: its POST does not show whether the server got the call.
Why
Some tool calls change things, such as creating a record or sending a message. Resending one after a dropped connection could do it twice, and this makes that less likely. You may see more failed calls that you need to check and retry yourself.