ToolCallStartEvent

Signals the start of a tool call.

Properties

Property	Type	Description
input?	JSONObject	Optional input value provided to the tool when executed.
inputSchema?	JSONValue	JSON schema describing the tool's input parameters. Present when requireConfirmation is true so the client can render an editable form.
isClientSideTool?	boolean	When true, this tool call should be executed locally by the client rather than server-side. The client should listen for ExecutingToolCallEvent via onExecutingToolCall, run the tool, and return the result with sendToolCallEnd.
metaData?	JSONObject	Optional metadata pertaining to the tool call.
outputSchema?	JSONValue	JSON Schema describing the tool's expected output. Present on client-side tool calls so the client can validate or render a form for the result before sending it back via sendToolCallEnd.
requireConfirmation?	boolean	Indicates that the tool call requires user confirmation before execution. When true, the client should render a confirmation UI and respond with a confirmToolCall event on the same tool call.
timestamp?	string	The time the tool call was made.
toolName	string	Identifies the tool that is to be called.