# HarnessContentBlockStartEvent
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Event indicating the start of a content block.

## Contents
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 ** contentBlockIndex **   <a name="BedrockAgentCore-Type-HarnessContentBlockStartEvent-contentBlockIndex"></a>
The index of the content block within the message.  
Type: Integer  
Required: Yes

 ** start **   <a name="BedrockAgentCore-Type-HarnessContentBlockStartEvent-start"></a>
The content block start payload.  
Type: [HarnessContentBlockStart](API_HarnessContentBlockStart.md) object  
 **Note: **This object is a Union. Only one member of this object can be specified or returned.  
Required: Yes

## See Also
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For more information about using this API in one of the language-specific AWS SDKs, see the following:
+  [AWS SDK for C\$1\$1](https://docs.aws.amazon.com/goto/SdkForCpp/bedrock-agentcore-2024-02-28/HarnessContentBlockStartEvent) 
+  [AWS SDK for Java V2](https://docs.aws.amazon.com/goto/SdkForJavaV2/bedrock-agentcore-2024-02-28/HarnessContentBlockStartEvent) 
+  [AWS SDK for Ruby V3](https://docs.aws.amazon.com/goto/SdkForRubyV3/bedrock-agentcore-2024-02-28/HarnessContentBlockStartEvent)