# Function isErr

Core exports - Types, Result<T,E>, errors, and logger Split from index.ts for file size compliance (Issue #285)

- isErr<T, E>(result: Result<T, E>): result is { ok: false; error: E }

  Type guard to check if a Result is in the Err state.

  #### Type Parameters

  - T

    The success value type

  - E

    The error value type

  #### Parameters

  - result: Result<T, E>

    The Result to check

  #### Returns result is { ok: false; error: E }

  True if the Result is Err

  - Defined in packages/nexus-agents/src/core/result.ts:73