Interface: ToolCallStartEvent<TToolName>#

Defined in: packages/ai/src/types.ts:1216

Emitted when a tool call starts.

@ag-ui/core provides: toolCallId, toolCallName, parentMessageId? TanStack AI adds: model?, toolName (deprecated alias), index?, metadata?

Field shapes are taken from AG-UI via Pick (not extends) so Zod .passthrough() index signatures do not pollute the StreamChunk discriminated union — required for TypedStreamChunk narrowing.

Extends#

• Pick<AGUIToolCallStartEvent, | "toolCallId" | "toolCallName" | "parentMessageId" | "timestamp" | "rawEvent">

Type Parameters#

TToolName#

TToolName extends string = string

Constrained tool name type. Defaults to string (untyped). When the stream is returned from chat() with typed tools, TypedStreamChunk intersects a literal onto toolCallName and toolName for discrimination.

Properties#

index?#

optional index?: number;

Defined in: packages/ai/src/types.ts:1234

Index for parallel tool calls

metadata?#

optional metadata?: Record<string, unknown>;

Defined in: packages/ai/src/types.ts:1239

Provider-specific metadata to carry into the ToolCall. Untyped at the event layer because events flow through a discriminated union that does not survive generics; adapters cast it to their typed TToolCallMetadata shape when emitting.

model?#

optional model?: string;

Defined in: packages/ai/src/types.ts:1224

Model identifier for multi-model support

toolName#

toolName: TToolName;

Defined in: packages/ai/src/types.ts:1232

Deprecated#

Use toolCallName instead (from @ag-ui/core spec). Kept for backward compatibility.

Carries TToolName on the base interface; for toolCallName narrowing use TypedStreamChunk (distributed variants intersect the AG-UI field).

type#

type: "TOOL_CALL_START";

Defined in: packages/ai/src/types.ts:1222