Annotations
Several components of the specification, like [Image Manifests](manifest.md) and [Descriptors](descriptor.md), feature an optional annotations property, whose format is common and defined in this section.
This property contains arbitrary metadata.
- Annotations MUST be a key-value map where both the key and value MUST be strings.
- While the value MUST be present, it MAY be an empty string.
- Keys MUST be unique within this map, and best practice is to namespace the keys.
- Keys SHOULD be named using a reverse domain notation - e.g. `com.example.myKey`.
- The prefix `org.opencontainers` is reserved for keys defined in Open Container Initiative (OCI) specifications and MUST NOT be used by other specifications and extensions.
- Keys using the `org.opencontainers.image` namespace are reserved for use in the OCI Image Specification and MUST NOT be used by other specifications and extensions, including other OCI specifications.
- If there are no annotations then this property MUST either be absent or be an empty map.
- Consumers MUST NOT generate an error if they encounter an unknown annotation key.
This specification defines the following annotation keys, intended for but not limited to [image index](image-index.md), image [manifest](manifest.md), and [descriptor](descriptor.md) authors.
- **org.opencontainers.image.created** date and time on which the image was built, conforming to [RFC 3339][rfc3339].
- **org.opencontainers.image.authors** contact details of the people or organization responsible for the image (freeform string)
- **org.opencontainers.image.url** URL to find more information on the image (string)
- **org.opencontainers.image.documentation** URL to get documentation on the image (string)
- **org.opencontainers.image.source** URL to get source code for building the image (string)
- **org.opencontainers.image.version** version of the packaged software
- The version MAY match a label or tag in the source code repository
- version MAY be [Semantic versioning-compatible](https://semver.org/)
- **org.opencontainers.image.revision** Source control revision identifier for the packaged software.
- **org.opencontainers.image.vendor** Name of the distributing entity, organization or individual.
- **org.opencontainers.image.licenses** License(s) under which contained software is distributed as an [SPDX License Expression][spdx-license-expression].
- **org.opencontainers.image.ref.name** Name of the reference for a target (string).
- SHOULD only be considered valid when on descriptors on `index.json` within [image layout](image-layout.md).
- Character set of the value SHOULD conform to alphanum of `A-Za-z0-9` and separator set of `-._:@/+`
- A valid reference matches the following [grammar](considerations.md#ebnf):
ref ::= component ("/" component)*
component ::= alphanum (separator alphanum)*
alphanum ::= [A-Za-z0-9]+
separator ::= [-._:@+] | "--"
- **org.opencontainers.image.title** Human-readable title of the image (string)
- **org.opencontainers.image.description** Human-readable description of the software packaged in the image (string)
- **org.opencontainers.image.base.digest** [Digest](descriptor.md#digests) of the image this image is based on (string)
- This SHOULD be the immediate image sharing zero-indexed layers with the image, such as from a Dockerfile `FROM` statement.
- This SHOULD NOT reference any other images used to generate the contents of the image (e.g., multi-stage Dockerfile builds).
- **org.opencontainers.image.base.name** Image reference of the image this image is based on (string)
- This SHOULD be image references in the format defined by [distribution/distribution][distribution-reference].
- This SHOULD be a fully qualified reference name, without any assumed default registry. (e.g., `registry.example.com/my-org/my-image:tag` instead of `my-org/my-image:tag`).
- This SHOULD be the immediate image sharing zero-indexed layers with the image, such as from a Dockerfile `FROM` statement.
- This SHOULD NOT reference any other images used to generate the contents of the image (e.g., multi-stage Dockerfile builds).
- If the `image.base.name` annotation is specified, the `image.base.digest` annotation SHOULD be the digest of the manifest referenced by the `image.ref.name` annotation.
[Label Schema][label-schema] defined a number of conventional labels for container images, and these are now superseded by annotations with keys starting **org.opencontainers.image**.
While users are encouraged to use the **org.opencontainers.image** keys, tools MAY choose to support compatible annotations using the **org.label-schema** prefix as follows.
| `org.opencontainers.image` prefix |
`org.label-schema` prefix |
Compatibility notes |
| `created` |
`build-date` |
Compatible |
| `url` |
`url` |
Compatible |
| `source` |
`vcs-url` |
Compatible |
| `version` |
`version` |
Compatible |
| `revision` |
`vcs-ref` |
Compatible |
| `vendor` |
`vendor` |
Compatible |
| `title` |
`name` |
Compatible |
| `description` |
`description` |
Compatible |
| `documentation` |
`usage` |
Value is compatible if the documentation is located by a URL |
| `authors` |
|
No equivalent in Label Schema |
| `licenses` |
|
No equivalent in Label Schema |
| `ref.name` |
|
No equivalent in Label Schema |
|
`schema-version` |
No equivalent in the OCI Image Spec |
|
`docker.*`, `rkt.*` |
No equivalent in the OCI Image Spec |
[distribution-reference]: https://github.com/distribution/distribution/blob/d0deff9cd6c2b8c82c6f3d1c713af51df099d07b/reference/reference.go
[label-schema]: https://github.com/label-schema/label-schema.org/blob/gh-pages/rc1.md
[rfc3339]: https://tools.ietf.org/html/rfc3339#section-5.6
[spdx-license-expression]: https://spdx.github.io/spdx-spec/v2.3/SPDX-license-expressions/