> For clean Markdown content of this page, append .md to this URL. For the complete documentation index, see https://buildwithfern.com/learn/llms.txt.

# Publish/Subscribe Operations

> Define AsyncAPI publish/subscribe operations for event-driven APIs. Step-by-step tutorial with message examples and bi-directional channels.

Operations in AsyncAPI are defined underneath the `operations` key, with channels defined under the `channels` key. Below is an example of defining publish and subscribe operations:

**`asyncapi.yml`**

```yml title="asyncapi.yml" maxLines=0 {2-22}
channels:
  user/notifications:
    address: user/notifications
    messages:
      UserNotification:
        $ref: '#/components/messages/UserNotification'

operations:
  onUserNotification:
    action: receive
    channel:
      $ref: '#/channels/user~1notifications'
    summary: Receive user notifications
    description: Subscribe to user notification events
  sendUserNotification:
    action: send
    channel:
      $ref: '#/channels/user~1notifications'
    summary: Send user notification
    description: Publish a user notification event
```

## Message examples

You can provide examples of messages by using the `examples` key in your message definitions:

**`asyncapi.yml`**

```yaml title="asyncapi.yml" {8-15}
components:
  messages:
    UserNotification:
      name: UserNotification
      title: User Notification
      summary: Notification sent to a user
      contentType: application/json
      payload:
        $ref: '#/components/schemas/Notification'
      examples:
        - name: EmailNotification
          summary: Example email notification
          payload:
            userId: "123e4567-e89b-12d3-a456-426614174000"
            type: "email"
            message: "Welcome to our service!"
            priority: "medium"
```

## Publish operations

Publish operations represent messages that your service sends to a channel:

**`asyncapi.yml`**

```yml title="asyncapi.yml" {2-8}
operations:
  publishOrderStatus:
    action: send
    channel:
      $ref: '#/channels/order~1status'
    summary: Publish order status update
    description: Send order status updates to subscribers
    message:
      $ref: '#/components/messages/OrderStatus'
```

## Subscribe operations

Subscribe operations represent messages that your service receives from a channel:

**`asyncapi.yml`**

```yml title="asyncapi.yml" {2-8}
operations:
  subscribeToUserSignups:
    action: receive
    channel:
      $ref: '#/channels/user~1signup'
    summary: Subscribe to user signups
    description: Receive notifications when users sign up
    message:
      $ref: '#/components/messages/UserSignup'
```

## Bi-directional communication

You can define both publish and subscribe operations for the same channel to enable bi-directional communication:

**`asyncapi.yml`**

```yml title="asyncapi.yml" {2-15}
operations:
  sendChatMessage:
    action: send
    channel:
      $ref: '#/channels/chat~1room'
    summary: Send chat message
    description: Send a message to a chat room
  receiveChatMessage:
    action: receive
    channel:
      $ref: '#/channels/chat~1room'
    summary: Receive chat message
    description: Receive messages from a chat room
```

> Define AsyncAPI publish/subscribe operations for event-driven APIs. Step-by-step tutorial with message examples and bi-directional channels.