About User ID Sync

  • Updated

Most companies in advertising technology set their own identifier in web pages often by using cookies.

Why You Need to Match Cookies

Because of the way browsers are designed, cookies set by a given company usually can't be read by other companies. For example, Adform sets an identifier that cannot be read by its partners.

If companies only worked with identifiers set by themselves, programmatic and data exchange functionality would be limited. Therefore, Adform would not be able to buy ads or data from its partners. For programmatic channels and data exchange to work, a company needs to share identification information. This is done through an ID matching process.


If Adform wants to match IDs with a partner (a site called "example.com").

  1. Adform identifies the partner with ID 123.

  2. Once the ID matching process starts, a pre-agreed matching pixel is triggered, similar to http://example.com/party=adform/sync?uid=123.

  3. As a result, Adform attaches a parameter to the example.com pixel (parameter UID=123).

  4. example.com can read their own identifier from the browser and build a matching table of example.com IDs mapped to Adform.com IDs.

The matching table can look like this:

example.com ID

Adform ID







Either Adform or example.com (or both) can store the matching table.

Programmatic Behavior

When Adform acts as an SSP and example.com acts as an DSP:

  1. A user visits the site tracked by the Adform SSP.

  2. Adform identifies the user as 123.

  3. Adform looks up for the example.com ID in the matching table (in this case, ABCD).

  4. A bid request with the ID ABCD is sent to example.com.

  5. Example.com bids on the known user.

How to Match Third-Party Cookies

  1. On your website, open your browser‘s developer tools on the page where the placement is being called.

    If the cookie exists, use its value for the matching process.

  2. In the developer's tools panel, click Network and filter out requests made by Adform (rp=).

  3. Open a request and navigate to the Header section.

  4. In Request Headers, look for the cookie UID in the browser.

  5. In Query string parameters look for CC=1. If this parameter exists, you can stop the process because the user has disabled cookies. If the parameter doesn‘t exist, proceed to the next step.

  6. Set the cookie UID with a random long value.

  7. Take the current URL, append CC=1, and redirect to it (go back to Step 1).

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