Storage is a commodity

S3-compatible APIs have become the de-facto standard for digital storage.

Common Bucket is a community initiative to define the useful subset of the API that is broadly support to improve interoperability across cloud providers and open-source tools.

Vendor Neutral

Write code once. Run it on AWS, Cloudflare, MinIO, or your own server. No proprietary SDK wrappers required.

Predictable Specs

A clearly defined subset of the 100+ S3 operations. If a tool claims "Common Bucket Compliant", you know exactly what works.

Compatibility Tiers

Compliance is divided into 3 tiers. To be considered "S3 Compatible", a service must fully implement Tier 1.

Tier 1: The Core

MANDATORY

The absolute minimum required for a system to function as an object store. Enables basic CRUD operations. Most static site generators and simple backup tools only need this.

PutObject

GetObject

DeleteObject

HeadObject

ListObjectsV2

CreateBucket

DeleteBucket

HeadBucket

Example: List Objects (Tier 1)

GET /?list-type=2&prefix=photos/2023/ HTTP/1.1
Host: my-bucket.s3.us-east-1.amazonaws.com
Date: Mon, 21 Nov 2025 16:00:00 GMT
Authorization: AWS4-HMAC-SHA256 ...

Tier 2: Reliability

RECOMMENDED

Essential for production workloads handling files larger than 100MB. Ensures reliability over unstable networks via multipart uploads.

CreateMultipartUpload

UploadPart

CompleteMultipartUpload

AbortMultipartUpload

ListParts

Tier 3: Application Logic

ADVANCED

Features required for complex application architectures, including presigned URLs for client-side uploads and custom metadata handling.

Presigned URLs Must support v4 signature generation and consumption.

User Metadata Handling of x-amz-meta-* headers.

Ecosystem Matrix

A living list of storage providers and open-source tools measured against the OpenS3 standard.

Open Source Tools

Tool	Tier 1	Tier 2	Tier 3	Docs
MinIO				Specs
Ceph (RGW)				Specs
Zenko (CloudServer)				Specs
Garage				Specs
SeaweedFS				Specs
OpenStack Swift				Specs

Cloud Services

Provider	Tier 1	Tier 2	Tier 3	Docs
AWS S3 (Reference)				Specs
Wasabi				Specs
Cloudflare R2				Specs
Backblaze B2				Specs
DigitalOcean Spaces				Specs
Scaleway Object Storage				Specs
Google Cloud Storage				Specs
Linode (Akamai)				Specs
IDrive e2				Specs
Tigris				Specs
Oracle Cloud (OCI)				Specs
IBM Cloud Object Storage				Specs

Compatibility Note

"Partial" support in Tier 3 often refers to inconsistencies in how providers handle CopyObject directives or specific headers in Presigned URLs. Always reference the vendor documentation linked above.