---
title: "workflow/errors"
description: Semantic error types thrown by the Workflow SDK and its storage backends.
type: overview
summary: Explore the error classes exported from workflow/errors for handling workflow failures.
related:
  - /docs/foundations/errors-and-retries
---

API reference for the error classes exported from the `workflow/errors` package.

All errors extend [`WorkflowError`](/docs/api-reference/workflow-errors/workflow-error), so you can catch any SDK error with a single `instanceof` check, or narrow to a specific class for fine-grained handling.

## Base classes

<Cards>
    <Card href="/docs/api-reference/workflow-errors/workflow-error" title="WorkflowError">
        Base class for all workflow error types.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/workflow-world-error" title="WorkflowWorldError">
        Base error for failures from workflow storage backends.
    </Card>
</Cards>

## Registration errors

<Cards>
    <Card href="/docs/api-reference/workflow-errors/workflow-not-registered-error" title="WorkflowNotRegisteredError">
        Thrown when a workflow function is not registered in the current deployment.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/step-not-registered-error" title="StepNotRegisteredError">
        Thrown when a step function is not registered in the current deployment.
    </Card>
</Cards>

## Run errors

<Cards>
    <Card href="/docs/api-reference/workflow-errors/workflow-run-not-found-error" title="WorkflowRunNotFoundError">
        Thrown when operating on a workflow run that does not exist.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/workflow-run-failed-error" title="WorkflowRunFailedError">
        Thrown when awaiting the return value of a failed workflow run.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/workflow-run-cancelled-error" title="WorkflowRunCancelledError">
        Thrown when awaiting the return value of a canceled workflow run.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/workflow-run-not-completed-error" title="WorkflowRunNotCompletedError">
        Thrown when requesting the result of a workflow run that has not completed yet.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/workflow-runtime-error" title="WorkflowRuntimeError">
        Thrown when the workflow runtime encounters an execution error, such as serialization failures or timeouts.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/run-expired-error" title="RunExpiredError">
        Thrown when a workflow run has expired and can no longer be operated on.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/run-not-supported-error" title="RunNotSupportedError">
        Thrown when a workflow run requires a newer workflow spec version than the installed SDK supports.
    </Card>
</Cards>

## Hook errors

<Cards>
    <Card href="/docs/api-reference/workflow-errors/hook-not-found-error" title="HookNotFoundError">
        Thrown when resuming a hook that does not exist.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/hook-conflict-error" title="HookConflictError">
        Thrown when creating a hook with a token that is already in use by another workflow run.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/hook-force-claimed-error" title="HookForceClaimedError">
        Thrown to a hook's awaiters when another run takes its token over with `experimental_force`.
    </Card>
</Cards>

## Backend errors

<Cards>
    <Card href="/docs/api-reference/workflow-errors/throttle-error" title="ThrottleError">
        Thrown when a request is rate-limited by the workflow backend.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/entity-conflict-error" title="EntityConflictError">
        Thrown when a storage operation conflicts with the current entity state.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/precondition-failed-error" title="PreconditionFailedError">
        Thrown when an event creation is rejected because the client's event-log snapshot is stale.
    </Card>
    <Card href="/docs/api-reference/workflow-errors/too-early-error" title="TooEarlyError">
        Thrown when a request is made before the system is ready to process it.
    </Card>
</Cards>