---
url: >-
  https://adk.nht.io/api/@nhtio/adk/exceptions/variables/E_TOOL_DOWNSTREAM_ERROR.md
description: >-
  Thrown (as a rejection reason) when a {@link @nhtio/adk!Tool}'s handler throws
  during execution.
---

# Variable: E\_TOOL\_DOWNSTREAM\_ERROR

```ts
const E_TOOL_DOWNSTREAM_ERROR: CreatedException<[]>;
```

Defined in: [lib/exceptions/runtime.ts:414](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/exceptions/runtime.ts#L414)

Thrown (as a rejection reason) when a [@nhtio/adk!Tool](../../forge/classes/Tool.md)'s handler throws during execution.

## Remarks

Not fatal — a downstream tool failure is a recoverable runtime condition. The tool call loop
catches this error specifically to report the failure back to the model rather than crashing
the pipeline.