# Processing data in a custom labeling workflow with Amazon Lambda
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In this topic, you can learn how to deploy optional [Amazon Lambda](https://www.amazonaws.cn/lambda/) functions when creating a custom labeling workflow. You can specify two types of Lambda functions to use with your custom labeling workflow.
+ *Pre-annotation Lambda*: This function pre-processes each data object sent to your labeling job prior to sending it to workers.
+ *Post-annotation Lambda*: This function processes the results once workers submit a task. If you specify multiple workers per data object, this function may include logic to consolidate annotations.

If you are a new user of Lambda and Ground Truth, we recommend that you use the pages in this section as follows:

1. First, review [Using pre-annotation and post-annotation Lambda functionsUsing Lambda functions](sms-custom-templates-step3-lambda-requirements.md).

1. Then, use the page [Add required permissions to use Amazon Lambda with Ground Truth](sms-custom-templates-step3-lambda-permissions.md) to learn about security and permission requirements to use your pre-annotation and post-annotation Lambda functions in a Ground Truth custom labeling job.

1. Next, you need to visit the Lambda console or use Lambda's APIs to create your functions. Use the section [Create Lambda functions using Ground Truth templates](sms-custom-templates-step3-lambda-create.md) to learn how to create Lambda functions.

1. To learn how to test your Lambda functions, see [Test pre-annotation and post-annotation Lambda functions](sms-custom-templates-step3-lambda-test.md).

1. After you create pre-processing and post-processing Lambda functions, select them from the **Lambda functions** section that comes after the code editor for your custom HTML in the Ground Truth console. To learn how to use these functions in a `CreateLabelingJob` API request, see [Create a Labeling Job (API)](sms-create-labeling-job-api.md).

For a custom labeling workflow tutorial that includes example pre-annotation and post-annotation Lambda functions, see [Demo template: Annotation of images with `crowd-bounding-box`](sms-custom-templates-step2-demo1.md).

**Topics**
+ [Using pre-annotation and post-annotation Lambda functions](sms-custom-templates-step3-lambda-requirements.md)
+ [Add required permissions to use Amazon Lambda with Ground Truth](sms-custom-templates-step3-lambda-permissions.md)
+ [Create Lambda functions using Ground Truth templates](sms-custom-templates-step3-lambda-create.md)
+ [Test pre-annotation and post-annotation Lambda functions](sms-custom-templates-step3-lambda-test.md)