---
title: EntityConflictError
description: Thrown when a storage operation conflicts with the current entity state.
type: reference
summary: Catch EntityConflictError when a world operation conflicts with entity state (e.g. duplicate events or runs).
related:
  - /docs/api-reference/workflow-errors/workflow-world-error
  - /docs/api-reference/workflow-errors/run-expired-error
---

`EntityConflictError` is thrown by world implementations when a storage operation conflicts with the current entity state. This includes cases like creating a run that already exists or writing an event that has already been persisted.

It corresponds to HTTP 409 Conflict semantics.

<Callout>
The Workflow runtime handles this error automatically during replay and event deduplication. You will only encounter it when interacting with world storage APIs directly.
</Callout>

```typescript lineNumbers
import { EntityConflictError } from "workflow/errors"
declare const world: { events: { create(...args: any[]): Promise<any> } }; // @setup
declare const runId: string; // @setup
declare const event: any; // @setup

try {
  await world.events.create(runId, event);
} catch (error) {
  if (EntityConflictError.is(error)) { // [!code highlight]
    // Event already exists — safe to ignore during replay
  }
}
```

## API Signature

### Properties

<TSDoc
definition={`
interface EntityConflictError {
  /** The error message. */
  message: string;
}
export default EntityConflictError;`}
/>

### Static Methods

#### `EntityConflictError.is(value)`

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

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

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