> ## Documentation Index
> Fetch the complete documentation index at: https://phaseo.app/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Lifecycle hooks

> React to run, model, step, tool, and checkpoint events.

Use `onEvent` to update product interfaces, write audit records, or connect agent activity to your existing telemetry.

## Listen to a run

```typescript theme={null}
const result = await agent.run({
  input,
  client,
  onEvent(event) {
    console.log(event.type, event.runId);
  },
});
```

Keep event handlers small. Move slow network or storage work onto your application's queue when it should not delay the run.

## Event families

| Family | Events                                                                                                |
| ------ | ----------------------------------------------------------------------------------------------------- |
| Run    | `run.started`, `run.resumed`, `run.waiting_for_human`, `run.cancelled`, `run.completed`, `run.failed` |
| Step   | `step.started`, `step.completed`, `step.failed`, `step.cancelled`                                     |
| Model  | `model.requested`, `model.completed`, `model.failed`                                                  |
| Tool   | `tool.started`, `tool.preliminary_result`, `tool.completed`, `tool.failed`                            |
| State  | `checkpoint.saved`                                                                                    |

`step.completed` is emitted after the completed step has been checkpointed. This lets a persistence or telemetry consumer treat it as a stable boundary.

## Choose events for a product interface

* Use model deltas from [Streaming](./agent-sdk-streaming) for live answer text.
* Use tool events for tool-call cards and progress indicators.
* Use `run.waiting_for_human` to show approval or input controls.
* Use terminal run events to close loading states and record outcomes.

## Related guides

* [Streaming](./agent-sdk-streaming)
* [State and approval](./agent-sdk-state-and-approval)
* [DevTools](./agent-sdk-devtools)