Annotations provide a place to store additional metadata for Kubernetes objects where the sole purpose of the metadata is assisting tools and libraries. They are a way for other programs driving Kubernetes via an API to store some opaque data with an object. Annotations can be used for the tool itself or to pass configuration information between external systems.

Annotation keys use the same format as label keys. However, because they are often used to communicate information between tools, the “namespace” part of the key is more important. Example keys include deployment.kubernetes.io/revision or kubernetes.io/change-cause. The value component of an annotation is a free-form string field.