diff --git a/packages/svelte/types/index.d.ts b/packages/svelte/types/index.d.ts
index 0822c02d6d..5520ccabe9 100644
--- a/packages/svelte/types/index.d.ts
+++ b/packages/svelte/types/index.d.ts
@@ -673,7 +673,49 @@ declare module 'svelte/attachments' {
 	 * @since 5.29
 	 */
 	export function createAttachmentKey(): symbol;
-	export function fromAction<Node extends HTMLElement, Parameter extends any>(...args: undefined extends NoInfer<Parameter> ? [action: (node: Node, parameter?: never) => void | ActionReturn<Parameter, Record<never, any>>, parameter?: (() => NoInfer<Parameter>) | undefined] : [action: (node: Node, parameter: Parameter) => void | ActionReturn<Parameter, Record<never, any>>, parameter: () => NoInfer<Parameter>]): Attachment<Node>;
+	export function fromAction<Node extends HTMLElement, Parameter extends any>(...args: undefined extends NoInfer<Parameter> ? [action: (node: Node, parameter?: never) => void | ActionReturn_1<Parameter, Record<never, any>>, parameter?: (() => NoInfer<Parameter>) | undefined] : [action: (node: Node, parameter: Parameter) => void | ActionReturn_1<Parameter, Record<never, any>>, parameter: () => NoInfer<Parameter>]): Attachment<Node>;
+	/**
+	 * Actions can return an object containing the two properties defined in this interface. Both are optional.
+	 * - update: An action can have a parameter. This method will be called whenever that parameter changes,
+	 *   immediately after Svelte has applied updates to the markup. `ActionReturn` and `ActionReturn<undefined>` both
+	 *   mean that the action accepts no parameters.
+	 * - destroy: Method that is called after the element is unmounted
+	 *
+	 * Additionally, you can specify which additional attributes and events the action enables on the applied element.
+	 * This applies to TypeScript typings only and has no effect at runtime.
+	 *
+	 * Example usage:
+	 * ```ts
+	 * interface Attributes {
+	 * 	newprop?: string;
+	 * 	'on:event': (e: CustomEvent<boolean>) => void;
+	 * }
+	 *
+	 * export function myAction(node: HTMLElement, parameter: Parameter): ActionReturn<Parameter, Attributes> {
+	 * 	// ...
+	 * 	return {
+	 * 		update: (updatedParameter) => {...},
+	 * 		destroy: () => {...}
+	 * 	};
+	 * }
+	 * ```
+	 */
+	interface ActionReturn_1<
+		Parameter = undefined,
+		Attributes extends Record<string, any> = Record<never, any>
+	> {
+		update?: (parameter: Parameter) => void;
+		destroy?: () => void;
+		/**
+		 * ### DO NOT USE THIS
+		 * This exists solely for type-checking and has no effect at runtime.
+		 * Set this through the `Attributes` generic instead.
+		 */
+		$$_attributes?: Attributes;
+	}
+
+	// Implementation notes:
+	// - undefined extends X instead of X extends undefined makes this work better with both strict and nonstrict mode
 
 	export {};
 }