AWS SDK Version 3 for .NET
API Reference

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Adds an object to a bucket. You must have WRITE permissions on a bucket to add an object to it.

Amazon S3 never adds partial objects; if you receive a success response, Amazon S3 added the entire object to the bucket. You cannot use PutObject to only update a single piece of metadata for an existing object. You must put the entire object with updated metadata if you want to update some values.

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. To prevent objects from being deleted or overwritten, you can use Amazon S3 Object Lock.

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, returns an error. Additionally, you can calculate the MD5 while putting an object to Amazon S3 and compare the returned ETag to the calculated MD5 value.

  • To successfully complete the PutObject request, you must have the s3:PutObject in your IAM permissions.

  • To successfully change the objects acl of your PutObject request, you must have the s3:PutObjectAcl in your IAM permissions.

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

  • The Content-MD5 header is required for any request to upload an object with a retention period configured using Amazon S3 Object Lock. For more information about Amazon S3 Object Lock, see Amazon S3 Object Lock Overview in the Amazon S3 User Guide.

You have four mutually exclusive options to protect data using server-side encryption in Amazon S3, depending on how you choose to manage the encryption keys. Specifically, the encryption key options are Amazon S3 managed keys (SSE-S3), Amazon Web Services KMS keys (SSE-KMS or DSSE-KMS), and customer-provided keys (SSE-C). Amazon S3 encrypts data with server-side encryption by using Amazon S3 managed keys (SSE-S3) by default. You can optionally tell Amazon S3 to encrypt data at rest by using server-side encryption with other key options. For more information, see Using Server-Side Encryption.

When adding a new object, you can use headers to grant ACL-based permissions to individual Amazon Web Services accounts or to predefined groups defined by Amazon S3. These permissions are then added to the ACL on the object. By default, all objects are private. Only the owner has full access control. For more information, see Access Control List (ACL) Overview and Managing ACLs Using the REST API.

If the bucket that you're uploading objects to uses the bucket owner enforced setting for S3 Object Ownership, ACLs are disabled and no longer affect permissions. Buckets that use this setting only accept PUT requests that don't specify an ACL or PUT requests that specify bucket owner full control ACLs, such as the bucket-owner-full-control canned ACL or an equivalent form of this ACL expressed in the XML format. PUT requests that contain other ACLs (for example, custom grants to certain Amazon Web Services accounts) fail and return a 400 error with the error code AccessControlListNotSupported. For more information, see Controlling ownership of objects and disabling ACLs in the Amazon S3 User Guide.

If your bucket uses the bucket owner enforced setting for Object Ownership, all objects written to the bucket by any account will be owned by the bucket owner.

By default, Amazon S3 uses the STANDARD Storage Class to store newly created objects. The STANDARD storage class provides high durability and high availability. Depending on performance needs, you can specify a different Storage Class. Amazon S3 on Outposts only uses the OUTPOSTS Storage Class. For more information, see Storage Classes in the Amazon S3 User Guide.

If you enable versioning for a bucket, Amazon S3 automatically generates a unique version ID for the object being stored. Amazon S3 returns this ID in the response. When you enable versioning for a bucket, if Amazon S3 receives multiple write requests for the same object simultaneously, it stores all of the objects. For more information about versioning, see Adding Objects to Versioning-Enabled Buckets. For information about returning the versioning state of a bucket, see GetBucketVersioning.

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