What
The internal validation for toolUses and toolResults data now checks for fields named tool_use_id and tool, rather than the previous id and name. The corresponding error messages were updated to match.
Why
This is a naming change to the fields expected in this data; anything constructing these payloads directly needs to use the new field names to pass validation.
Names in the bundletool_use_id
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 Run Claude Code programmatically touched a line naming tool_use_id after this was published.
When you enable either option, Claude Code forwards messages from [subagents at every nesting depth](/docs/en/sub-agents#let-subagents-spawn-their-own-subagents), whether each one was spawned with the Agent tool or started as a [forked ski…headless see the edit
Confirmed since
Anthropic's documentation has since written up tool_use_id, on Beta.
When set, this event was cross-posted from a subagent's thread to surface its custom tool use on the primary thread's stream. Empty on the thread's own events. Informational only: the server routes the matching `user.custom_tool_result` by…api/beta 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 tool_use_id, on Beta.