---
title: A/B testing with same-URL direct access · Cloudflare Workers docs
description: Set up an A/B test by controlling what response is served based on cookies. This version supports passing the request through to test and control on the origin, bypassing random assignment.
lastUpdated: 2025-04-15T13:29:20.000Z
source_url:
  html: https://a74404c8.preview.developers.cloudflare.com/workers/examples/ab-testing/index.md
  md: https://a74404c8.preview.developers.cloudflare.com/workers/examples/ab-testing/
---

* JavaScript

  ```js
  const NAME = "myExampleWorkersABTest";


  export default {
    async fetch(req) {
      const url = new URL(req.url);


      // Enable Passthrough to allow direct access to control and test routes.
      if (url.pathname.startsWith("/control") || url.pathname.startsWith("/test"))
        return fetch(req);


      // Determine which group this requester is in.
      const cookie = req.headers.get("cookie");


      if (cookie && cookie.includes(`${NAME}=control`)) {
        url.pathname = "/control" + url.pathname;
      } else if (cookie && cookie.includes(`${NAME}=test`)) {
        url.pathname = "/test" + url.pathname;
      } else {
        // If there is no cookie, this is a new client. Choose a group and set the cookie.
        const group = Math.random() < 0.5 ? "test" : "control"; // 50/50 split
        if (group === "control") {
          url.pathname = "/control" + url.pathname;
        } else {
          url.pathname = "/test" + url.pathname;
        }
        // Reconstruct response to avoid immutability
        let res = await fetch(url);
        res = new Response(res.body, res);
        // Set cookie to enable persistent A/B sessions.
        res.headers.append("Set-Cookie", `${NAME}=${group}; path=/`);
        return res;
      }
      return fetch(url);
    },
  };
  ```

* TypeScript

  ```ts
  const NAME = "myExampleWorkersABTest";


  export default {
    async fetch(req): Promise<Response> {
      const url = new URL(req.url);
      // Enable Passthrough to allow direct access to control and test routes.
      if (url.pathname.startsWith("/control") || url.pathname.startsWith("/test"))
        return fetch(req);
      // Determine which group this requester is in.
      const cookie = req.headers.get("cookie");
      if (cookie && cookie.includes(`${NAME}=control`)) {
        url.pathname = "/control" + url.pathname;
      } else if (cookie && cookie.includes(`${NAME}=test`)) {
        url.pathname = "/test" + url.pathname;
      } else {
        // If there is no cookie, this is a new client. Choose a group and set the cookie.
        const group = Math.random() < 0.5 ? "test" : "control"; // 50/50 split
        if (group === "control") {
          url.pathname = "/control" + url.pathname;
        } else {
          url.pathname = "/test" + url.pathname;
        }
        // Reconstruct response to avoid immutability
        let res = await fetch(url);
        res = new Response(res.body, res);
        // Set cookie to enable persistent A/B sessions.
        res.headers.append("Set-Cookie", `${NAME}=${group}; path=/`);
        return res;
      }
      return fetch(url);
    },
  } satisfies ExportedHandler;
  ```

* Python

  ```py
  import random
  from urllib.parse import urlparse, urlunparse
  from workers import Response, fetch


  NAME = "myExampleWorkersABTest"


  async def on_fetch(request):
      url = urlparse(request.url)
      # Uncomment below when testing locally
      # url = url._replace(netloc="example.com") if "localhost" in url.netloc else url


      # Enable Passthrough to allow direct access to control and test routes.
      if url.path.startswith("/control") or url.path.startswith("/test"):
          return fetch(urlunparse(url))


      # Determine which group this requester is in.
      cookie = request.headers.get("cookie")


      if cookie and f'{NAME}=control' in cookie:
          url = url._replace(path="/control" + url.path)
      elif cookie and f'{NAME}=test' in cookie:
          url = url._replace(path="/test" + url.path)
      else:
          # If there is no cookie, this is a new client. Choose a group and set the cookie.
          group = "test" if random.random() < 0.5 else "control"
          if group == "control":
              url = url._replace(path="/control" + url.path)
          else:
              url = url._replace(path="/test" + url.path)


          # Reconstruct response to avoid immutability
          res = await fetch(urlunparse(url))
          headers = dict(res.headers)
          headers["Set-Cookie"] = f'{NAME}={group}; path=/'
          return Response(res.body, headers=headers)


      return fetch(urlunparse(url))
  ```

* Hono

  ```ts
  import { Hono } from "hono";
  import { getCookie, setCookie } from "hono/cookie";


  const app = new Hono();


  const NAME = "myExampleWorkersABTest";


  // Enable passthrough to allow direct access to control and test routes
  app.all("/control/*", (c) => fetch(c.req.raw));
  app.all("/test/*", (c) => fetch(c.req.raw));


  // Middleware to handle A/B testing logic
  app.use("*", async (c) => {
    const url = new URL(c.req.url);


    // Determine which group this requester is in
    const abTestCookie = getCookie(c, NAME);


    if (abTestCookie === "control") {
      // User is in control group
      url.pathname = "/control" + c.req.path;
    } else if (abTestCookie === "test") {
      // User is in test group
      url.pathname = "/test" + c.req.path;
    } else {
      // If there is no cookie, this is a new client
      // Choose a group and set the cookie (50/50 split)
      const group = Math.random() < 0.5 ? "test" : "control";


      // Update URL path based on assigned group
      if (group === "control") {
        url.pathname = "/control" + c.req.path;
      } else {
        url.pathname = "/test" + c.req.path;
      }


      // Set cookie to enable persistent A/B sessions
      setCookie(c, NAME, group, {
        path: "/",
      });
    }


    const res = await fetch(url);


    return c.body(res.body, res);
  });


  export default app;
  ```
