AWS SDK Version 3 for .NET
API Reference

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Adds an object to a bucket.

Amazon S3 is a distributed system. If it receives multiple write requests for the same object simultaneously, it overwrites all but the last object written. However, Amazon S3 provides features that can modify this behavior:

  • General purpose bucket permissions - The following permissions are required in your policies when your PutObject request includes specific headers.

    • s3:PutObject - To successfully complete the PutObject request, you must always have the s3:PutObject permission on a bucket to add an object to it.

    • s3:PutObjectAcl - To successfully change the objects ACL of your PutObject request, you must have the s3:PutObjectAcl.

    • s3:PutObjectTagging - To successfully set the tag-set with your PutObject request, you must have the s3:PutObjectTagging.

  • Directory bucket permissions - To grant access to this API operation on a directory bucket, we recommend that you use the CreateSession API operation for session-based authorization. Specifically, you grant the s3express:CreateSession permission to the directory bucket in a bucket policy or an IAM identity-based policy. Then, you make the CreateSession API call on the bucket to obtain a session token. With the session token in your request header, you can make API requests to this operation. After the session token expires, you make another CreateSession API call to generate a new session token for use. Amazon Web Services CLI or SDKs create session and refresh the session token automatically to avoid service interruptions when a session expires. For more information about authorization, see CreateSession.

Data integrity with Content-MD5
  • General purpose bucket - To ensure that data is not corrupted traversing the network, use the Content-MD5 header. When you use this header, Amazon S3 checks the object against the provided MD5 value and, if they do not match, Amazon S3 returns an error. Alternatively, when the object's ETag is its MD5 digest, you can calculate the MD5 while putting the object to Amazon S3 and compare the returned ETag to the calculated MD5 value.

  • Directory bucket - This functionality is not supported for directory buckets.

HTTP Host header syntax

Directory buckets - The HTTP Host header syntax is

For more information about related Amazon S3 APIs, see the following:


This is an asynchronous operation using the standard naming convention for .NET 4.5 or higher. For .NET 3.5 the operation is implemented as a pair of methods using the standard naming convention of BeginPutObject and EndPutObject.

Namespace: Amazon.S3
Assembly: AWSSDK.S3.dll
Version: 3.x.y.z


public abstract Task<PutObjectResponse> PutObjectAsync(
         PutObjectRequest request,
         CancellationToken cancellationToken


Type: Amazon.S3.Model.PutObjectRequest

Container for the necessary parameters to execute the PutObject service method.

Type: System.Threading.CancellationToken

A cancellation token that can be used by other objects or threads to receive notice of cancellation.

Return Value

The response from the PutObject service method, as returned by S3.

Version Information

.NET Core App:
Supported in: 3.1

.NET Standard:
Supported in: 2.0

.NET Framework:
Supported in: 4.5

See Also