# ChatMiddlewarePhase

# Type Alias: ChatMiddlewarePhase

```ts
type ChatMiddlewarePhase = 
  | "init"
  | "beforeModel"
  | "modelStream"
  | "beforeTools"
  | "afterTools"
  | "structuredOutput";
```

Defined in: [packages/ai/src/activities/chat/middleware/types.ts:25](https://github.com/TanStack/ai/blob/main/packages/ai/src/activities/chat/middleware/types.ts#L25)

Phase of the chat middleware lifecycle.
- 'init': Initial config transform before the chat engine starts
- 'beforeModel': Before each adapter chatStream call (per agent iteration)
- 'modelStream': During model streaming
- 'beforeTools': Before tool execution phase
- 'afterTools': After tool execution phase
- 'structuredOutput': During the final structured-output adapter call (set
  for chunks from adapter.structuredOutputStream or the synthesized fallback)