diff --git a/cheetah.ts b/cheetah.ts
index 6dcca29..0cc739b 100644
--- a/cheetah.ts
+++ b/cheetah.ts
@@ -69,6 +69,7 @@ export class cheetah extends base<cheetah>() {
   #proxy
   #routes: Set<[Uppercase<Method>, string, RegExp, HandlerOrSchema[]]>
   #runtime: 'deno' | 'cloudflare'
+  #onPlugIn
 
   constructor({
     base,
@@ -109,6 +110,7 @@ export class cheetah extends base<cheetah>() {
     this.#runtime = typeof globalThis?.Deno?.serve !== 'function'
       ? 'cloudflare'
       : 'deno'
+    this.#onPlugIn = false
   }
 
   /* use ---------------------------------------------------------------------- */
@@ -242,6 +244,32 @@ export class cheetah extends base<cheetah>() {
       let body: Response | void = undefined
 
       for (const e of this.#extensions.values()) {
+        if (this.#onPlugIn === true && e[1].onPlugIn !== undefined) {
+          await e[1].onPlugIn({
+            env: __app.env,
+            routes: this.#routes,
+            runtime: this.#runtime,
+            setRoute: (method, pathname, ...handlers) => {
+              this.#routes.add([
+                method.toUpperCase() as Uppercase<Method>,
+                pathname,
+                RegExp(
+                  `^${
+                    (pathname
+                      .replace(/\/+(\/|$)/g, '$1'))
+                      .replace(/(\/?\.?):(\w+)\+/g, '($1(?<$2>*))')
+                      .replace(/(\/?\.?):(\w+)/g, '($1(?<$2>[^$1/]+?))')
+                      .replace(/\./g, '\\.')
+                      .replace(/(\/?)\*/g, '($1.*)?')
+                  }/*$`,
+                ),
+                // @ts-ignore:
+                handlers,
+              ])
+            },
+          })
+        }
+
         if (
           e[0] !== '*' &&
           __app.request.pathname.indexOf(e[0]) !== 0
@@ -249,10 +277,12 @@ export class cheetah extends base<cheetah>() {
           continue
         }
 
-        const { onRequest } = e[1]
-
-        if (onRequest !== undefined) {
-          const result = await onRequest({ app: __app, req, _: e[1].__config })
+        if (e[1].onRequest !== undefined) {
+          const result = await e[1].onRequest({
+            app: __app,
+            req,
+            _: e[1].__config,
+          })
 
           if (result !== undefined) {
             body = result
@@ -260,6 +290,10 @@ export class cheetah extends base<cheetah>() {
         }
       }
 
+      if (this.#onPlugIn) {
+        this.#onPlugIn = false
+      }
+
       if (body !== undefined) {
         return body
       }
diff --git a/extensions.ts b/extensions.ts
index 5e52253..66d8f96 100644
--- a/extensions.ts
+++ b/extensions.ts
@@ -1,5 +1,8 @@
 // Copyright 2023 Samuel Kopp. All rights reserved. Apache-2.0 license.
+import { ZodString, ZodUnion } from 'https://deno.land/x/zod@v3.21.4/types.ts'
+import { Handler, ObjectType } from './handler.ts'
 import { AppContext, Context } from './mod.ts'
+import { Method } from './base.ts'
 
 type HasRequired<T> = Partial<T> extends T ? false : true
 
@@ -10,6 +13,76 @@ export type Extension<
   Config extends Record<string, unknown> | unknown = never,
 > = {
   __config: Config | undefined
+  onPlugIn: HasRequired<Config> extends true ? ((context: {
+      env: AppContext['env']
+      routes: AppContext['routes']
+      runtime: AppContext['runtime']
+      setRoute: <
+        Pathname extends `/${string}`,
+        // deno-lint-ignore no-explicit-any
+        ValidatedBody extends ObjectType | ZodString | ZodUnion<any>,
+        ValidatedCookies extends ObjectType,
+        ValidatedHeaders extends ObjectType,
+        ValidatedQuery extends ObjectType,
+      >(
+        method: Method,
+        pathname: Pathname,
+        ...handler: (
+          | {
+            body?: ValidatedBody
+            cookies?: ValidatedCookies
+            headers?: ValidatedHeaders
+            query?: ValidatedQuery
+            /** @deprecated please pass this option to the `c.req.body()` method! */
+            transform?: boolean // TODO remove at v2.0
+            cors?: string
+          }
+          | Handler<
+            Pathname,
+            ValidatedBody,
+            ValidatedCookies,
+            ValidatedHeaders,
+            ValidatedQuery
+          >
+        )[]
+      ) => void | Promise<void>
+      settings: Config
+    }) => void | Promise<void>)
+    : ((context: {
+      env: AppContext['env']
+      routes: AppContext['routes']
+      runtime: AppContext['runtime']
+      setRoute: <
+        Pathname extends `/${string}`,
+        // deno-lint-ignore no-explicit-any
+        ValidatedBody extends ObjectType | ZodString | ZodUnion<any>,
+        ValidatedCookies extends ObjectType,
+        ValidatedHeaders extends ObjectType,
+        ValidatedQuery extends ObjectType,
+      >(
+        method: Method,
+        pathname: Pathname,
+        ...handlers: (
+          | {
+            body?: ValidatedBody
+            cookies?: ValidatedCookies
+            headers?: ValidatedHeaders
+            query?: ValidatedQuery
+            /** @deprecated please pass this option to the `c.req.body()` method! */
+            transform?: boolean // TODO remove at v2.0
+            cors?: string
+          }
+          | Handler<
+            Pathname,
+            ValidatedBody,
+            ValidatedCookies,
+            ValidatedHeaders,
+            ValidatedQuery
+          >
+        )[]
+      ) => void
+      settings?: Config
+    }) => void | Promise<void>)
   onRequest?: HasRequired<Config> extends true ? ((context: {
       app: AppContext
       req: Request
@@ -51,15 +124,18 @@ export function validExtension(ext: Record<string, unknown>) {
 export function createExtension<
   Config extends Record<string, unknown> | unknown = unknown,
 >({
+  onPlugIn,
   onRequest,
   onResponse,
 }: {
+  onPlugIn?: Extension<Config>['onPlugIn']
   onRequest?: Extension<Config>['onRequest']
   onResponse?: Extension<Config>['onResponse']
 }) {
   return ((__config?: Config) => {
     return {
       __config,
+      onPlugIn,
       onRequest,
       onResponse,
       [Symbol('cheetah.extension')]: 'v1.0',