diff --git a/index.d.ts b/index.d.ts
index e16fce9..4910b37 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -1,111 +1,131 @@
 import type { FastifyPluginCallback, RouteOptions, HTTPMethods } from 'fastify'
 
-interface OverviewStructureSource {
-  stackIndex: number,
-  fileName: string,
-  relativeFileName: string,
-  lineNumber: number,
-  columnNumber: number,
-  functionName: string,
-  typeName?: string,
-  methodName?: string,
+declare module 'fastify' {
+  export interface FastifyInstance {
+    overview: <T = {}, D extends Record<PropertyKey, unknown> = {}>(opts?: fastifyOverview.FastifyOverviewDecoratorOptions) => fastifyOverview.OverviewStructure<T, D>;
+  }
 }
 
-interface OverviewStructureDecorator {
-  name: string;
-  type: 'undefined' | 'object' | 'boolean' | 'number' | 'bigint' | 'string' | 'symbol' | 'function' | 'array'
-  source?: OverviewStructureSource,
-}
+type FastifyOverview = FastifyPluginCallback<fastifyOverview.FastifyOverviewOptions>
 
-interface OverviewStructureHook {
-  name: string;
-  hash: string;
-  source?: OverviewStructureSource;
-}
+declare namespace fastifyOverview {
+  export interface OverviewStructureSource {
+    stackIndex: number,
+    fileName: string,
+    relativeFileName: string,
+    lineNumber: number,
+    columnNumber: number,
+    functionName: string,
+    typeName?: string,
+    methodName?: string,
+  }
 
-interface OverviewStructureHooks {
-  onRequest?: OverviewStructureHook[],
-  preParsing?: OverviewStructureHook[],
-  preValidation?: OverviewStructureHook[],
-  preHandler?: OverviewStructureHook[],
-  preSerialization?: OverviewStructureHook[],
-  onError?: OverviewStructureHook[],
-  onSend?: OverviewStructureHook[],
-  onResponse?: OverviewStructureHook[],
-  onTimeout?: OverviewStructureHook[],
-  onListen?: OverviewStructureHook[],
-  onReady?: OverviewStructureHook[],
-  preClose?: OverviewStructureHook[],
-  onClose?: OverviewStructureHook[],
-  onRoute?: OverviewStructureHook[],
-  onRegister?: OverviewStructureHook[],
-  onRequestAbort?: OverviewStructureHook[],
-}
+  export interface OverviewStructureDecorator {
+    name: string;
+    type: 'undefined' | 'object' | 'boolean' | 'number' | 'bigint' | 'string' | 'symbol' | 'function' | 'array'
+    source?: OverviewStructureSource,
+  }
 
-interface RouteItem {
-  method: HTTPMethods | HTTPMethods[],
-  url: string,
-  prefix: string,
-  hooks: OverviewStructureHooks,
-  source?: OverviewStructureSource,
-}
+  export interface OverviewStructureHook {
+    name: string;
+    hash: string;
+    source?: OverviewStructureSource;
+  }
 
-export interface OverviewStructure<T = {}> {
-  id: Number,
-  name: string,
-  source?: OverviewStructureSource,
-  children?: OverviewStructure<T>[],
-  decorators?: {
-    decorate: OverviewStructureDecorator[],
-    decorateRequest: OverviewStructureDecorator[],
-    decorateReply: OverviewStructureDecorator[]
-  },
-  hooks?: OverviewStructureHooks,
-  routes?: (Omit<RouteItem, keyof T> & T)[]
-}
+  export interface OverviewStructureHooks {
+    onRequest?: OverviewStructureHook[],
+    preParsing?: OverviewStructureHook[],
+    preValidation?: OverviewStructureHook[],
+    preHandler?: OverviewStructureHook[],
+    preSerialization?: OverviewStructureHook[],
+    onError?: OverviewStructureHook[],
+    onSend?: OverviewStructureHook[],
+    onResponse?: OverviewStructureHook[],
+    onTimeout?: OverviewStructureHook[],
+    onListen?: OverviewStructureHook[],
+    onReady?: OverviewStructureHook[],
+    preClose?: OverviewStructureHook[],
+    onClose?: OverviewStructureHook[],
+    onRoute?: OverviewStructureHook[],
+    onRegister?: OverviewStructureHook[],
+    onRequestAbort?: OverviewStructureHook[],
+  }
 
-export interface FastifyOverviewOptions {
-  /**
-   * Add a `source` property to each node of the tree.
-   * @default false
-   */
-   addSource?: boolean,
-
-  /**
-   * Expose a route that will return the JSON structure.
-   * By default the route is exposed at `GET /json-overview`.
-   * @default false
-   */
-   exposeRoute?: boolean,
-
-  /**
-   * Customize the route's options when `exposeRoute` is set to `true`
-   */
-   exposeRouteOptions?: Partial<RouteOptions>,
-
-  /**
-   * Customise which properties of the route options will be included in the overview
-   */
-  onRouteDefinition?: (routeOptions: RouteOptions & { routePath: string; path: string; prefix: string }) => Record<string, unknown>
-}
+  export interface RouteItem {
+    method: HTTPMethods | HTTPMethods[],
+    url: string,
+    prefix: string,
+    hooks: OverviewStructureHooks,
+    source?: OverviewStructureSource,
+  }
 
-export interface FastifyOverviewDecoratorOptions {
-  /**
-   * Filters routes based on the provided predicate
-   */
-   routesFilter?: (routeItem: RouteItem) => boolean,
-  /**
-   * To keep the structure light and clean, you can hide empty properties
-   * @default false
-   */
-   hideEmpty?: boolean,
-}
+  export interface Decorators {
+    instance?: Record<string, unknown>
+    request?: Record<string, unknown>
+    reply?: Record<string, unknown>
+  }
 
-declare module 'fastify' {
-  export interface FastifyInstance {
-    overview: <T = {}>(opts?: FastifyOverviewDecoratorOptions) => OverviewStructure<T>;
+  type ExtractDecoratorType<T extends Record<PropertyKey, unknown>, K extends keyof Decorators> = T extends Decorators ? T[K] : T
+
+  export interface OverviewStructure<T = {}, D extends Record<PropertyKey, unknown> = {}> {
+    id: Number,
+    name: string,
+    source?: OverviewStructureSource,
+    children?: OverviewStructure<T>[],
+    decorators?: {
+      decorate: (Omit<OverviewStructureDecorator, keyof ExtractDecoratorType<D, 'instance'>> & ExtractDecoratorType<D, 'instance'>)[],
+      decorateRequest: (Omit<OverviewStructureDecorator, keyof ExtractDecoratorType<D, 'request'>> & ExtractDecoratorType<D, 'request'>)[],
+      decorateReply: (Omit<OverviewStructureDecorator, keyof ExtractDecoratorType<D, 'reply'>> & ExtractDecoratorType<D, 'reply'>)[]
+    },
+    hooks?: OverviewStructureHooks,
+    routes?: (Omit<RouteItem, keyof T> & T)[]
+  }
+
+  export interface FastifyOverviewOptions {
+    /**
+     * Add a `source` property to each node of the tree.
+     * @default false
+     */
+    addSource?: boolean,
+
+    /**
+     * Expose a route that will return the JSON structure.
+     * By default the route is exposed at `GET /json-overview`.
+     * @default false
+     */
+    exposeRoute?: boolean,
+
+    /**
+     * Customize the route's options when `exposeRoute` is set to `true`
+     */
+    exposeRouteOptions?: Partial<RouteOptions>,
+
+    /**
+     * Customise which properties of the route options will be included in the overview
+     */
+    onRouteDefinition?: (routeOptions: RouteOptions & { routePath: string; path: string; prefix: string }) => Record<string, unknown>
+
+    /**
+     * Customise which information from decorators should be added to the overview
+     */
+    onDecorateDefinition?: (type: 'decorate' | 'decorateRequest' | 'decorateReply', name: string, value: unknown) => Record<string, unknown>
   }
+
+  export interface FastifyOverviewDecoratorOptions {
+    /**
+     * Filters routes based on the provided predicate
+     */
+    routesFilter?: (routeItem: RouteItem) => boolean,
+    /**
+     * To keep the structure light and clean, you can hide empty properties
+     * @default false
+     */
+    hideEmpty?: boolean,
+  }
+
+  export const fastifyOverview: FastifyOverview
+  export { fastifyOverview as default }
 }
 
-export const FastifyOverview: FastifyPluginCallback<FastifyOverviewOptions>
-export default FastifyOverview
+declare function fastifyOverview(...params: Parameters<FastifyOverview>): ReturnType<FastifyOverview>
+export = fastifyOverview