Server-side Cookies

Implementing first-party cookies to resolve third-party cookie browser restrictions

Privacy concerns are at an all-time high, and browsers have begun enforcing limitations on third-party cookie functionality. In 2019, Safari started forcing a 7-day expiration for third-party cookies, and Firefox started blocking them by default. In Q1 of 2024, Google Chrome started blocking third-party cookies for 1% of its users by default, increasing to all users in H2 of 2024.

How does this affect you?

Without third-party cookies to identify them, visitors are considered new users. In Safari this happens 7 days after the most recent visit, and if cookies are completely blocked, the visitor is considered a new user upon every pageview. The implications can be significant: An inflated number of users, broken variation stickiness in A/B testing, detached historical data, and more.

To overcome this limitation, you must serve the DYID cookie from your server, making it a first-party cookie that is not affected by the new restrictions.

How to serve the DYID cookie from your server


This solution is generic. See the next section to learn how to implement the solution in Shopify.

The DYID cookie must be set by the backend application serving your website on your domain. Cookies set this way are considered first-party cookies, and are therefore not affected by restrictions and can have a longer expiration period. Set this up in the code as follows:

  1. Check whether the visitor arrives at your site with a DYID cookie (is a returning user).
  2. If so, duplicate the cookie with a new name (_dyid_server), and set its expiration date to 1 year.


Let’s say the value of the _dyid cookie is 7237284912004766755. Duplicate the cookie value into a new cookie, _dyid_server, and set the expiration to 1 year by setting 31556951 as the max-age attribute value.

The result is the following cookie: _dyid_server=7237284912004766755;max-age=31556951

Here's a flow of this solution:

  1. A user enters your website.
  2. Your server (backend application) gets a request to return a web page from the browser. Requests from returning users include the _dyid cookie.
  3. Your application server performs the following steps:
    1. It checks whether the request includes a _dyid cookie.
    2. If the _dyid cookie is found, it duplicates it as a new _dyid_server cookie.
    3. It then returns the new cookie as a response header, with a 1-year expiration date.
      This sets it as a server-side first-party cookie in the user's browser, which is not affected by the cookie expiration enforcement.
      (Note that the _dyid cookie continues to be returned, this should not change).
  4. Our script now uses the _dyid_server cookie as it runs on your page, and your user sees the rendered content of your website.

This way, no returning user data is lost, even if the user has not visited your site in more than 7 days.

Note that if you have enabled Active Cookie Consent mode, it's important to wait for the consent object and act upon its result. Otherwise, you might write cookies for opted-out users.

Code examples

Here are some sample code snippets for commonly used platforms and programming languages.


>>> curl -v --cookie "_dyid=-3233584359067736988"                                                                                                                                                                                                                                                                                        19:55:13
*   Trying
* Connected to ( port 80 (#0)
> GET / HTTP/1.1
> Host:
> User-Agent: curl/7.64.1
> Accept: */*
> Cookie: _dyid=-3233584359067736988
< HTTP/1.1 200 OK
< Date: Mon, 30 Mar 2020 16:55:16 GMT
< Content-Type: text/html; charset=ISO-8859-1
< Set-Cookie: _dyid_server=-3233584359067736988; expires=Wed, 29-Apr-2021 16:55:16 GMT; path=/;; Secure

NodeJS (using Express and CookieParser)

// need cookieParser middleware before we can do anything with cookies
app.use((req, res, next) => {
  if (req.cookies._dyid) { // if this is a returning user and the DYID cookie exists
    const dyid = req.cookies._dyid;
    res.cookie('_dyid_server', dyid, { // store a new server-side cookie named "_dyid_server" with the DYID value
      expires: new Date( + 31540000000000), // Set a 1 year expiration for the new cookie

Python (using Django)

dyid_cookie = request.COOKIES.get('_dyid') 
if dyid_cookie is not None: # if this is a returning user and the DYID cookie exists
    set_cookie(‘_dyid_server’, dyid_cookie, 31557600) # Store a new server-side cookie named "_dyid_server" with the DYID value...


if(isset($_COOKIE['_dyid'])) {
 $dyid_cookie = $_COOKIE['_dyid']; /* if this is a returning user and the DYID cookie exists */
 setcookie('_dyid_server', $dyid_cookie, time() + 31557600); /* expire in 1 year */

Implementing DYID as a first-party cookie in Shopify

Shopify offers a simple way to implement a first-party cookie:

  1. In your Shopify admin, click Settings.
  2. Click Customer Events.
  3. Click Add Custom Pixel.
  4. Copy and paste the following code:
(async function(){
  const max_age = 30240000;
  const dyid_server = await browser.cookie.get("_dyid_server");
  if (
    dyid_server &&
    dyid_server !== "" &&
    dyid_server !== "null" &&
    dyid_server !== null
  ) {
  } else {
    const dyid = await browser.localStorage.getItem("_dyid");
    if (dyid) {

Technical validation

This procedure checks that the _dyid_server server-side cookie is created with the same value as the _dyid cookie, but with a 1-year expiration date. It can be done on any browser, but we used Chrome in this example:

  1. Open a new browser window and navigate to any page on your website that has the Dynamic Yield script.
  2. Open Chrome developer tools (press Command+Option+J (Mac) or Control+Shift+J (Windows, Linux, Chrome OS).
  3. Go to the Network tab. Select Preserve Log and then click Clear ⊘ .
  1. Refresh the page. Select the first request with the URL of your site (a), and look at the Headers tab (b).
  1. Verify that the value of _dyid_server is the same as the value of _dyid.
    The value of the _dyid_server cookie is in the request header. You can also find the value of _dyid in the Request Headers section of the Headers tab under "cookie:" (the first field). If the values match, your solution is verified.


This validation cannot be done in the Application Tab › Storage › Cookies area because this area includes both server-side and client-side cookies, so some of these will be automatically deleted by Safari.

Dynamic Yield by Mastercard Chrome extension

If third-party cookies are blocked due to Google's stricter third-party cookie policy, several capabilities relating to editing and debugging content on your site won't work. Learn more about our solution for overcoming this restriction.