additionalPrinterColumns

additionalPrinterColumns is a feature of Kubernetes CustomResourceDefinition (CRD) that enables administrators to tailor the tabular output of kubectl get for custom resources. By defining extra columns, users can surface important fields from the resource’s spec or status directly in the listing, improving at-a-glance visibility without inspecting each item individually. The values for these columns are obtained from the resource’s JSON using JSONPath expressions.

In Kubernetes API conventions, the column definitions are defined per version. In modern CRDs (apiextensions.k8s.io/v1), they appear under spec.versions[].additionalPrinterColumns. Each entry is a CustomResourceColumnDefinition and typically includes fields such as name, type, jsonPath, and optional description or format. The jsonPath selects the value to render in that column; the type indicates the data type (for example string, integer, boolean, date). The resulting header in kubectl corresponds to the name, and the cell contents are derived from the matching path in each resource instance. If a jsonPath does not resolve, the column may appear empty for that item.

Example usage:

apiVersion: apiextensions.k8s.io/v1

kind: CustomResourceDefinition

metadata:

name: foos.example.com

spec:

group: example.com

versions:

- name: v1

served: true

storage: true

additionalPrinterColumns:

- name: Replicas

type: integer

jsonPath: .spec.replicas

- name: Age

type: date

jsonPath: .metadata.creationTimestamp

scope: Namespaced

names:

plural: foos

singular: foo

kind: Foo

Limitations include that these columns are for kubectl display and do not affect resource storage or validation, and they rely on consistent JSONPath access to the fields. They may not be supported by all tools beyond kubectl.