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# Message Metadata
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Application-specific data that can be attached to Slack messages to enable rich interactive experiences and custom workflows.
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## Capabilities
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### Message Metadata
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Attach custom application data to messages for enhanced functionality and context.
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```typescript { .api }
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/**
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 * Application-specific data to attach to Slack message.
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 * @see https://docs.slack.dev/messaging/message-metadata
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 */
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interface MessageMetadata {
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  /** Human readable alphanumeric string representing your application's metadata event */
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  event_type: string;
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  /** Free-form object containing whatever data your application wishes to attach */
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  event_payload: {
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    [key: string]: string | number | boolean | MessageMetadataEventPayloadObject | MessageMetadataEventPayloadObject[];
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  };
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}
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interface MessageMetadataEventPayloadObject {
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  [key: string]: string | number | boolean;
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}
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```
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**Usage Examples:**
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```typescript
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import { MessageMetadata } from "@slack/types";
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// Task management metadata
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const taskMetadata: MessageMetadata = {
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  event_type: "task_created",
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  event_payload: {
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    task_id: "task_12345",
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    priority: "high",
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    assignee: "U123456789",
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    due_date: "2024-01-15",
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    completed: false,
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    tags: ["urgent", "backend"]
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  }
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};
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// Survey metadata
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const surveyMetadata: MessageMetadata = {
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  event_type: "survey_response",
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  event_payload: {
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    survey_id: "survey_67890",
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    response_count: 5,
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    average_rating: 4.2,
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    questions: [
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      { question_id: "q1", response: "Very satisfied" },
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      { question_id: "q2", response: "Would recommend" }
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    ]
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  }
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};
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// Using with message posting
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const message = {
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  channel: "C1234567890",
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  text: "New task has been created",
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  metadata: taskMetadata
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};
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```
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### Integration with Events
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Message metadata integrates with the Events API, allowing applications to react to metadata changes:
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```typescript
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// Message events with metadata
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interface MessageEvent {
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  type: 'message';
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  channel: string;
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  user: string;
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  text: string;
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  ts: string;
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  metadata?: MessageMetadata;
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}
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```
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### Best Practices
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- **Event Type Naming**: Use descriptive, consistent naming for `event_type` values
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- **Payload Structure**: Keep payloads flat when possible for better performance
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- **Data Types**: Use appropriate primitive types (string, number, boolean)
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- **Size Limits**: Be mindful of message size limits when attaching metadata
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- **Privacy**: Don't include sensitive information in metadata as it may be visible to developers