Migrating from server-side cookie to client-side cookie

We strongly advise our clients to no longer use a server-side cookie to measure visitors, and to instead move to measuring via client-side cookies.

We have made this choice for different reasons:

• Greater reliability when tracking unique visitors. Internet users are increasingly blocking (whether deliberately or not) third-party cookies (standard server-side cookies case). Safari, Opera and Firefox (private browsing) in particular block third-party cookies by default – a manual and deliberate action is required to authorise them.
• Lighter network traffic. To place our server-side cookie, our servers require redirection (invisible) to validate the placing of the cookie. This redirection causes an additional call from your site. Moving to client-side cookies makes it possible to avoid triggering this additional query.
• More consistent measurement methods. Measurement done via our mobile SDKs is systematically based on a client-side ID, as mobile applications cannot manage cookies. Moving to client-side cookies for the web makes it possible to unify how unique visitors are managed across different platforms. This also makes it possible to avoid handling specific cases for browsers that refuse third-party cookies, and to avoid having two types of tracking on a single site.

This migration will have several different impacts from an implementation and analysis point of view:

• Resetting new visitors. As the IDs of your unique visitors will all be new, our calculations will consider all visitors as new visitors once the switch is made. This phenomenon will disappear after your users visit a second time.
• Potential drop in number of unique visitors. Thanks to more reliable tracking of unique visitors, a user who may have previously been counted twice, due to refusal of third-party cookies, will now be effectively identified upon subsequent visits.
• Tagging via redirection will no longer be available. Campaign tagging via redirection, as well as clicks and impressions using /go. or /get. type URLs, cannot be used with first-party cookies.

To migrate, simply edit the corresponding option in your Tag Composer settings:

1. Tick the box for the Client-side user ID feature, if this is not already the case (box is ticked by default)
2. Edit the configuration for this feature, using the gear wheel icon to the right
3. Set the Mode to Always

An example of a configuration using client-side cookies: