---
title: WorkflowRuntimeError
description: Thrown when the workflow runtime encounters an execution error, such as serialization failures or timeouts.
type: reference
summary: Catch WorkflowRuntimeError for runtime-level failures like unserializable values or workflow timeouts.
related:
  - /docs/foundations/serialization
  - /docs/foundations/errors-and-retries
---

`WorkflowRuntimeError` is thrown when the workflow runtime encounters an error executing a workflow. Common causes include:

- Values crossing the workflow/step boundary that cannot be serialized
- Workflow execution timeouts
- Invalid runtime state, such as misconfigured streams

```typescript lineNumbers
import { WorkflowRuntimeError } from "workflow/errors"
declare function runWorkflowOperation(): Promise<void>; // @setup

try {
  await runWorkflowOperation();
} catch (error) {
  if (WorkflowRuntimeError.is(error)) { // [!code highlight]
    console.error("Workflow runtime error:", error.message);
  }
}
```

## API signature

### Properties

<TSDoc
definition={`
interface WorkflowRuntimeError {
  /** The error message. */
  message: string;
  /** The underlying cause, when provided. */
  cause?: unknown;
}
export default WorkflowRuntimeError;`}
/>

### Static methods

#### `WorkflowRuntimeError.is(value)`

Type-safe check for `WorkflowRuntimeError` instances. Preferred over `instanceof` because it works across module boundaries and VM contexts.

```typescript
import { WorkflowRuntimeError } from "workflow/errors"
declare const error: unknown; // @setup

if (WorkflowRuntimeError.is(error)) {
  // error is typed as WorkflowRuntimeError
}
```