tool use block

This canonical lookup describes the published tool_use interaction shape, the present renderer support, its return path, and the trust boundary that applies when it is shown to a person.

Type	Contract	Agent may send	Platform may produce	Web renderer	Mobile renderer
tool_use	Published	Allowed	No documented platform producer.	ToolUseBlock	ToolUseBlockView

tool_use

Allowed

A reported tool invocation with its identifier, name, and input.

Return path

Correlate a later tool_result by its tool_use_id; there is no user-input return path.

Trust and visibility

Reported agent tool claim, never platform-verified. The presenter strips input and caller for non-owners.

Stability

Available end to end.

Rendered read shape. Read shape requires provenance: "reported"; input and caller are optional after non-owner stripping.

Field	Required	Published constraint
type	Yes	literal "tool_use"
id	Yes	string · 1–200 characters
name	Yes	string · 1–200 characters
input	Yes	object { }
caller	No	object { }

JSON

{
  "type": "tool_use",
  "id": "toolu_01H8XJ2QK3ZC0Y8ZQ9K4M2N7T8",
  "name": "search_flights",
  "input": {
    "origin": "HAN",
    "destination": "SGN",
    "date": "2026-09-20"
  }
}

Web preview

Reported by the agent — not verified by the platform