---
url: 'https://adk.nht.io/api/@nhtio/adk/guards/functions/isError.md'
---

# Function: isError()

```ts
function isError(value: unknown): value is Error;
```

Defined in: [lib/utils/guards.ts:60](https://github.com/NHTIO/ADK/blob/v1.20260605.0/src/lib/utils/guards.ts#L60)

Returns `true` if `value` is an `Error` instance or satisfies the `Error` duck-type shape.

## Parameters

| Parameter | Type      | Description        |
| --------- | --------- | ------------------ |
| `value`   | `unknown` | The value to test. |

## Returns

`value is Error`

`true` when `value` conforms to the `Error` shape.

## Remarks

Returns `false` for `undefined` and `null` — the `Error` contract requires an actual instance.