@freelensapp/example-extension

Overview

This repository serves as an example and template for building and publishing extensions for the Freelens application.

It demonstrates how to add support for custom Kubernetes resources by implementing cluster pages, list views, and detail panels for Custom Resource Definitions (CRDs). Each resource is accessible from the Freelens sidebar, with status conditions, spec fields, and related objects displayed in the detail view.

Notable patterns demonstrated in this repository:

• Multiple API versions of the same CRD -- the Example resource is implemented for both v1alpha1 and v1alpha2, each with separate typed interfaces, detail views, list pages, and context menu items. The v1alpha1 to v1alpha2 migration also illustrates a field rename with inverted semantics (active to suspended).

• Auto-detection of the available API version -- the createAvailableVersionPage helper tries each registered version in priority order at runtime, renders the page for the first version whose store is available in the cluster, and shows a friendly message if the CRD is not installed.

• Static methods instead of instance methods -- Freelens creates plain object copies of Kubernetes resources rather than class instances, so all per-object logic is implemented as static methods on the KubeObject subclass (e.g. Example.getActive(object)).

• Error boundary with withErrorPage -- every component render is wrapped in a withErrorPage(props, fn) helper that catches errors, logs them, and renders a graceful error UI instead of crashing the panel.

• Persisted preferences with MobX -- ExamplePreferencesStore shows how to persist extension settings across restarts using Common.Store.ExtensionStore with MobX @observable fields.

Visit the wiki page about creating extensions for more information.

Requirements

• Kubernetes >= 1.24
• Freelens >= 1.8.0

Supported APIs

example.freelens.app

API Version	Kind	Scope	Description
v1alpha1	Example	Namespaced	Example custom resource (v1alpha1)
v1alpha2	Example	Namespaced	Example custom resource (v1alpha2)

To install Custom Resource Definitions for this example run:

kubectl apply -k examples/v1alpha1/crds
kubectl apply -k examples/v1alpha2/crds

Example resources for testing:

kubectl apply -k examples/v1alpha2/test
# or
kubectl apply -k examples/v1alpha1/test

Install

To install, open Freelens and go to Extensions (ctrl+shift+E or cmd+shift+E), then search for and install @freelensapp/example-extension.

Alternatively, open the following URL in the browser to install directly:

freelens://app/extensions/install/%40freelensapp%2Fexample-extension

Build from the source

You can build the extension from this repository.

Prerequisites

Use NVM, mise-en-place, or windows-nvm to install the required Node.js version.

From the root of this repository:

nvm install
# or
mise install
# or
winget install CoreyButler.NVMforWindows
nvm install 24.15.0
nvm use 24.15.0

Install pnpm:

corepack install
# or
curl -fsSL https://get.pnpm.io/install.sh | sh -
# or
winget install pnpm.pnpm

Build extension

pnpm i
pnpm build
pnpm pack

One script to build and pack the extension for testing:

pnpm pack:dev

Install built extension

The tarball will be placed in the current directory. In Freelens, navigate to the Extensions page and provide the path to the tarball, or drag and drop the .tgz file into the Freelens window.

Check code statically

pnpm lint:check

or

pnpm trunk:check

and

pnpm build
pnpm knip:check

Testing the extension with unpublished Freelens

In the Freelens working repository:

rm -f *.tgz
pnpm i
pnpm build
pnpm pack -r

Then in the extension repository:

echo "overrides:" >> pnpm-workspace.yaml
for i in ../freelens/*.tgz; do
  name=$(tar zxOf $i package/package.json | yq -r .name)
  echo "  \"$name\": $i" >> pnpm-workspace.yaml
done

pnpm clean:node_modules
pnpm build

License

Copyright (c) 2025-2026 Freelens Authors.

MIT License