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R2 implements some extensions on top of the basic S3 API. This page outlines these additional, available features.

Extended metadata using Unicode

The Workers R2 API supports Unicode in keys and values natively without requiring any additional encoding or decoding for the customMetadata field. These fields map to the x-amz-meta--prefixed headers used within the R2 S3-compatible API endpoint.

HTTP header names and values may only contain ASCII characters, which is a small subset of the Unicode character library. To easily accommodate users, R2 adheres to RFC2047 and automatically decodes all x-amz-meta-* header values before storage. On retrieval, any metadata values with unicode are RFC2047-encoded before rendering the response. The length limit for metadata values is applied to the decoded Unicode value.

These headers map to the httpMetadata field in the R2 bindings:

HTTP HeaderProperty Name

If using Unicode in object key names, refer to the Unicode Interoperability technical notes .


MERGE metadata directive

The x-amz-metadata-directive allows a MERGE value, in addition to the standard COPY and REPLACE options. When used, MERGE is a combination of COPY and REPLACE, which will COPY any metadata keys from the source object and REPLACE those that are specified in the request with the new value. You cannot use MERGE to remove existing metadata keys from the source — use REPLACE instead.