What
When a connection to an MCP server (Model Context Protocol, used to connect Claude Code to external tools and data) fails, the status output now includes an error_code field giving a specific reason, such as a rejected claude.ai login token, a rejected first-party Anthropic credential, or a connection that's pending approval.
Why
This makes it clear why an MCP connection is failing, such as needing to sign in again, instead of just showing a generic failure with no explanation.
Names in the bundleerror_code
Documented inapi/agents-and-tools/tool-use/advisor-tool
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Added since
A small documentation edit on Escalate hard decisions with the advisor tool touched a line naming error_code after this was published.
* **Unavailable**: the advisor call failed, and the line reads `Advisor unavailable (<error_code>)`, where `<error_code>` is the code the call returned.advisor see the edit
Confirmed since
Anthropic's documentation has since written up error_code, on Monitoring.
| MCP server connect or failure | `mcp_server_connection` | `status`, `server_name`, `is_plugin`, `error_code` |monitoring-usage see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up error_code, on Monitoring.