[API reference](https://evolu.dev/docs/api-reference) › [@evolu/common](https://evolu.dev/docs/api-reference/common) › [Result](https://evolu.dev/docs/api-reference/common/Result) › isErr

```ts
function isErr<T, E>(result: Result<T, E>): result is Err<E>;
```

Defined in: [packages/common/src/Result.ts:321](https://github.com/evoluhq/evolu/blob/e7144e2bbe9069362b62dec1b64a8aa922b8f1b0/packages/common/src/Result.ts#L321)

Type guard for [Err](https://evolu.dev/docs/api-reference/common/Result/interfaces/Err) results.