Adservers with the ability to access advertiser cookies and vice versa when both are serving from the advertiser's domain are provided, thereby avoiding the overhead and delay in backend cookie synchronization efforts. Further, advertising cookie data can be gathered regardless of whether a user is browsing a publisher's web site with an advertisement served by an adserver, or browsing the advertiser's web site, because the cookies were previously set when the user visited the advertiser's web site in the context of a first-party cookie. Even if the user has configured his or her browser to limit the setting of third-party cookies, the cookies can still be read by the adserver. By making cookie and advertising data immediately available in real time to both the advertiser and the adserver, the solution also provides for instantaneous and accurate targeting of web advertising to allow an educated ad selection process by either party.