# Using cost allocation S3 bucket tags
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To track the storage cost or other criteria for individual projects or groups of projects, label your Amazon S3 buckets using cost allocation tags. A *cost allocation tag* is a key-value pair that you associate with an S3 bucket. After you activate cost allocation tags, Amazon uses the tags to organize your resource costs on your cost allocation report. Cost allocation tags can only be used to label buckets. For information about tags used for labeling objects, see [Categorizing your objects using tags](object-tagging.md).

The *cost allocation report* lists the Amazon usage for your account by product category and linked account user. The report contains the same line items as the detailed billing report (see [Understanding your Amazon billing and usage reports for Amazon S3](aws-usage-report-understand.md)) and additional columns for your tag keys.

Amazon provides two types of cost allocation tags, an Amazon-generated tag and user-defined tags. Amazon defines, creates, and applies the Amazon-generated `createdBy` tag for you after an Amazon S3 CreateBucket event. You define, create, and apply *user-defined* tags to your S3 bucket.

You must activate both types of tags separately in the Billing and Cost Management console before they can appear in your billing reports. For more information about Amazon-generated tags, see [Amazon-Generated Cost Allocation Tags](https://docs.amazonaws.cn/awsaccountbilling/latest/aboutv2/aws-tags.html). 

For more information about activating tags, see [Using cost allocation tags](https://docs.amazonaws.cn/awsaccountbilling/latest/aboutv2/cost-alloc-tags.html) in the *Amazon Billing User Guide*.

**User-defined cost allocation tags**  
A user-defined cost allocation tag has the following components:
+ The tag key. The tag key is the name of the tag. For example, in the tag project/Trinity, project is the key. The tag key is a case-sensitive string that can contain 1 to 128 Unicode characters. 
+ The tag value. The tag value is a required string. For example, in the tag project/Trinity, Trinity is the value. The tag value is a case-sensitive string that can contain from 0 to 256 Unicode characters.

For details on the allowed characters for user-defined tags and other restrictions, see [User-Defined Tag Restrictions](https://docs.amazonaws.cn/awsaccountbilling/latest/aboutv2/allocation-tag-restrictions.html) in the *Amazon Billing User Guide*. For more information about user-defined tags, see [User-Defined Cost Allocation Tags](https://docs.amazonaws.cn/awsaccountbilling/latest/aboutv2/custom-tags.html) in the *Amazon Billing User Guide*.

**S3 bucket tags**  
Each S3 bucket has a tag set. A *tag set* contains all of the tags that are assigned to that bucket. A tag set can contain as many as 50 tags, or it can be empty. Keys must be unique within a tag set, but values in a tag set don't have to be unique. For example, you can have the same value in tag sets named project/Trinity and cost-center/Trinity.

Within a bucket, if you add a tag that has the same key as an existing tag, the new value overwrites the old value.

Amazon doesn't apply any semantic meaning to your tags. We interpret tags strictly as character strings. 

To add, list, edit, or delete tags, you can use the Amazon S3 console, the Amazon Command Line Interface (Amazon CLI), or the Amazon S3 API. 

## Managing tags for general purpose buckets
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You can add or manage tags for general purpose buckets using the Amazon S3 Console, the Amazon Command Line Interface (CLI), the Amazon SDKs, or using the S3 APIs. For more information, see the following.

**Using the Amazon S3 Console**  
To create tags in the console, see:
+ [Viewing the properties for an S3 general purpose bucket](view-bucket-properties.md).

**Using the API**  
To manage tags using the Amazon S3 API, see the following API pages in the *Amazon Simple Storage Service API Reference*.
+ [PutBucketTagging](https://docs.amazonaws.cn/AmazonS3/latest/API/API_PutBucketTagging.html)
+ [GetBucketTagging](https://docs.amazonaws.cn/AmazonS3/latest/API/API_GetBucketTagging.html)
+ [DeleteBucketTagging](https://docs.amazonaws.cn/AmazonS3/latest/API/API_DeleteBucketTagging.html)

**Note**  
After you enable ABAC, the `PutBucketTagging` or `DeleteBucketTagging` operations will no longer work. Instead, use the `TagResource` and `UntagResource` APIs to add or delete tags on your buckets. We recommend you use the `TagResource` and `UntagResource` APIs to manage tagging before enabling ABAC on your buckets. To learn more about ABAC, see[Enabling ABAC in general purpose buckets](buckets-tagging-enable-abac.md).

**Using the CLI**  
To manage tags using the Amazon CLI, see the following pages in the Amazon CLI Command Reference.
+ [put-bucket-tagging](https://docs.amazonaws.cn/cli/latest/reference/s3api/put-bucket-tagging.html)
+ [get-bucket-tagging](https://docs.amazonaws.cn/cli/latest/reference/s3api/get-bucket-tagging.html)
+ [delete-bucket-tagging](https://docs.amazonaws.cn/cli/latest/reference/s3api/delete-bucket-tagging.html)

## More Info
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+ [ Using Cost Allocation Tags](https://docs.amazonaws.cn/awsaccountbilling/latest/aboutv2/cost-alloc-tags.html) in the *Amazon Billing User Guide*
+ [Understanding your Amazon billing and usage reports for Amazon S3](aws-usage-report-understand.md)
+ [Amazon Billing reports for Amazon S3](aws-billing-reports.md)