What
Names and actions that you type or that arrive from a caller are now passed through a sanitiser before being placed into the error text sent back, instead of being embedded raw. This covers the inline /mcp command and the rejection messages for event submissions, so a crafted name cannot inject its own content into the message you or a client sees.
Details
/mcpsanitises both the action and the server name you typed when building its unrecognised-action message and its unknown-server message, the latter readingThere's no MCP server named ".- The action
/mcprecords in telemetry is sanitised the same way, not just the action shown on screen. - Event submissions refused for using a reserved name, with text noting the name
is reserved for a server-authored producer, and those refused for a name mismatch, both sanitise the caller-supplied name before it reaches the error string. - The remaining checks on event submissions are untouched: the cap on envelope size, the accepted authority values, and the provenance check on sender text all behave as before.
Evidence
There's no MCP server named ", is reserved for a server-authored producer
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
Names in the bundle/mcp
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 Channels reference touched a line naming /mcp after this was published.
* **`curl` succeeds but nothing reaches Claude**: run `/mcp` in your session to check the server's status. A `failed` status usually means a dependency or import error in your server file. To see the stderr trace, restart with `claude --de…channels-reference see the edit
Confirmed since
Anthropic's documentation has since written up /mcp, on Third party connectors with remote MCP.
**MCP server URL**: the HTTPS address where the server accepts MCP requests, for example `https://mcp.example.com/mcp`. After you continue, Claude checks the URL and pre-fills the authentication settings it detects, marked "Detected."connectors/custom/remote-mcp see the edit
Two sources agreeTwo things we can check say the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up /mcp, on Third party connectors with remote MCP.
Anthropic's release notes agree
Fixed /mcp listing a project .mcp.json entry that declares the claude.ai connector type under the trusted "claude.ai" heading; it now…