general-create-extension-type

name	general-create-extension-type
description	Create a new extension type for the Umbraco backoffice extension registry. Use when adding a new type of extension that can be registered via manifests (e.g., a new dashboard type, a new sidebar app type, a new toolbar extension type). Any package can define extension types.
allowed-tools	Read, Write, Edit, Grep, Glob

Create Extension Type

Create a new extension type for the Umbraco backoffice extension registry.

What you need from the user

1. Type name — The type string used in manifests (e.g., 'dashboard', 'searchProvider')
2. Purpose — What this extension type does (determines which base interface to extend)
3. Meta shape — What configuration the extension needs from consumers
4. Whether it needs conditions — Should extensions of this type support conditional loading?
5. Whether it has an element, API, or both — Does it render UI, provide logic, or both?

Files to create

All files go in the relevant feature directory (e.g., src/packages/my-package/my-feature/).

my-feature/
├── my-feature.extension.ts     # Type definition + global declaration
├── my-feature-element.interface.ts  # Element interface (if element-based)
└── types.ts                    # Meta interface (if needed)

Step 1: Choose the base manifest interface

Your extension...	Extend from	Import
Renders a custom element	ManifestElement<T>	@umbraco-cms/backoffice/extension-api
Provides an API class (no UI)	ManifestApi<T>	@umbraco-cms/backoffice/extension-api
Has both element and API	ManifestElementAndApi<E, A>	@umbraco-cms/backoffice/extension-api
Needs conditional loading	Also extend ManifestWithDynamicConditions<UmbExtensionConditionConfig>	@umbraco-cms/backoffice/extension-api

Step 2: Define the manifest interface

// my-feature.extension.ts
import type { ManifestElement, ManifestWithDynamicConditions } from '@umbraco-cms/backoffice/extension-api';

export interface MetaMyFeature {
	label?: string;
	// ... properties consumers configure via meta
}

export interface ManifestMyFeature
	extends ManifestElement<UmbMyFeatureElement>,
		ManifestWithDynamicConditions<UmbExtensionConditionConfig> {
	type: 'myFeature';
	meta: MetaMyFeature;
}

declare global {
	interface UmbExtensionManifestMap {
		umbMyFeature: ManifestMyFeature;
	}
}

Key rules

• The type property must be a string literal type (not string)
• The key in UmbExtensionManifestMap must be unique across the entire codebase
• The declare global block is what makes the registry type-aware — without it, the type won't be recognized

Step 3: Define the element/API interface (if needed)

// my-feature-element.interface.ts
import type { UmbElement } from '@umbraco-cms/backoffice/element-api';

export interface UmbMyFeatureElement extends UmbElement {
	// Properties/methods that implementations must provide
}

Step 4: If the type supports kinds

Add a union type for the base manifest plus kind-specific variants:

export interface ManifestMyFeatureButtonKind extends ManifestMyFeature {
	type: 'myFeature';
	kind: 'button';
	meta: MetaMyFeatureButtonKind;
}

export interface MetaMyFeatureButtonKind extends MetaMyFeature {
	icon: string;
}

// Union all variants in the global declaration
declare global {
	interface UmbExtensionManifestMap {
		umbMyFeature: ManifestMyFeature | ManifestMyFeatureButtonKind;
	}
}

Step 5: Export from the package barrel

Add the type export to the package's index.ts:

export type * from './my-feature/my-feature.extension.js';

Use export type * since these are type-only exports.

Step 6: Register manifests that use this type

Verify the type works by creating a test manifest:

const manifest: UmbExtensionManifest = {
	type: 'myFeature',
	alias: 'Umb.MyFeature.Test',
	name: 'Test My Feature',
	element: () => import('./my-feature-test.element.js'),
	meta: {
		label: 'Test',
	},
};

TypeScript should provide autocomplete for type and validate meta against MetaMyFeature.

Checklist

• Manifest interface extends the correct base (ManifestElement, ManifestApi, or ManifestElementAndApi)
• type property is a string literal, not string
• declare global block adds to UmbExtensionManifestMap with a unique key
• Meta interface is defined separately and exported
• Element/API interface is defined if the type renders UI or provides logic
• If kinds are supported: kind-specific interfaces extend the base with literal kind property
• Type is exported from the package's index.ts
• Compiles: npm run compile