> For the complete documentation index, see [llms.txt](https://docs.rootcause.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rootcause.ai/more-details/applications/application-modules/onappevent.md).

# On application event

> Start a flow when another application in this workspace emits a declared event.

Starts a flow when another application in this workspace emits a declared event.

The subscribe half of the pair EmitEvent publishes: `applicationId` and `name` say which event, and `filter` narrows it to the payloads worth waking for. Durable only, because the event has to survive nobody having the page open.

## At a glance

|                          |                        |
| ------------------------ | ---------------------- |
| Module type              | `OnAppEvent`           |
| Category                 | Events                 |
| Default tier             | `durable`              |
| Runs on                  | `durable`              |
| Starts a flow            | yes                    |
| Holds a body             | no                     |
| Keeps state between runs | no                     |
| Available in             | every application type |

## Parameters

### `name`

`string` · required · defaults to `""`

The event name it emits.

### `applicationId`

`string` · required · defaults to `""`

The application to subscribe to.

### `concurrency`

`"replace" | "skip" | "queue"` · required · defaults to `"queue"`

What to do when the previous run is still going.

### `filter`

`object` · optional · defaults to `null`

Narrow the subscription to payloads matching these clauses. Each is a `path` into the payload, an `operator` of `eq`, `neq` or `contains`, and the `value` to test.

## Inputs

*None.*

## Outputs

| Port    | Kind    | Connects to     | Description                                                      |
| ------- | ------- | --------------- | ---------------------------------------------------------------- |
| `event` | `event` | `event`, `json` | The event envelope, carrying the emitting application's payload. |

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