Private Click Measurement (PCM)

Private Click Measurement (PCM) is a Webkit development to enable privacy-friendly tracking. It should prevent the collection of personal data and at the same time enable conversion tracking with reference to a clicked ad - even if the user has not consented to the consent banner.

It is active in Apple’s Safari browser and from iOS 14.5 also in iOS or iPadOS apps.
Webkit proposed the PCM to the World Wide Web Consortium (W3C) as a standard and hopes it will be supported in other browsers.


To ensure the data privacy, some restrictions (compared to normal tracking pixels) are necessary:

  • There is no user mapping possible and therefore no capturing demographic User features
  • The time of the conversion is transmitted, not the time of the ad click
  • The attribution reports are transmitted with a delay, randomly in a time window between 24 and 48 hours after the respective event (or even later when the user browser is running again)
  • With an ad-click, an 8-bit ID can be transmitted (a number between 0 and 255, i.e. 256 possible values / campaigns) - per domain
  • For a conversion, a 4-bit ID is transmitted (a number between 00 and 15, i.e. 16 different types of conversion) - per domain
    A kind of priority specification should also be possible later here
  • The attribution window is a maximum of 7 days, i.e. if the conversion takes place later than 7 days after the ad click, it will not be tracked

How it works

Technically, PCM can look like this in the HTML source text of the source page using the example of a website ad:



  attributionsourceid="[8-Bit (Campaign) ID]"


>Ad Text</a>

If a conversion takes place, the shop may send a GET request back to the source page in the following form:[4-Bit (Conversion) ID]

It is then clear that a conversion has taken place and of which conversion type, but the assignment to the campaign is still missing. As already mentioned, this is only sent between 24 and 48 hours later (or even later) for data protection reasons.

A more detailed description of the functional principle can be found on this page: