Unclear The header's name, and which requests pass the check that adds it, are not known.
What
A tool call is a single action Claude takes with a tool. When Claude Code sends an authorized request to an MCP server (a Model Context Protocol server, which gives Claude extra tools) and knows which tool call the request belongs to, it can now add a header containing that tool call's ID. Any value already in that header is replaced. This happens only when a further check on the request passes.
Before, these requests carried only an authorization header and one other header.
Why
A server reached this way can link each request to the specific tool call that caused it.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
The header's name, and which requests pass the check that adds it, are not known.