I had some issues getting the v3 AWS SDK for JavaScript to communicate with localstack S3, but I found a solution! With the V2 JS SDK, the configuration object for the S3 client looks like: { "region": "eu-west-1", "endpoint": "http://localhost:4566", "s3ForcePathStyle": true } The last field tells the sdk not to use .hostname style connections, and instead puts the bucket in the path. For local..