Ad tracking, explained without the jargon

Plain-language definitions of the terms that come up when you try to work out why your ad reporting stopped matching your sales. Written for shop owners, not engineers.

• Conversions API

  The Conversions API, often shortened to CAPI, is the interface Meta provides for a shop to report a sale from its own server rather than from the shopper's browser. Because the report leaves a server, an ad blocker or a browser privacy setting cannot stop it, which is why sales the pixel loses still reach Meta.

• Event Match Quality

  Event Match Quality is a score from 1 to 10 that Meta gives each event a shop sends, measuring how well Meta could match that event to a real person. It is graded on the customer details attached to the event, such as email, phone and location, and a low score means fewer sales get matched to an ad.

• Server-side tracking

  Server-side tracking means a shop reports events to an ad platform from its own server rather than from the shopper's browser. Because the report never passes through the browser, ad blockers and browser privacy limits do not apply to it, and the report can carry details the browser never had, such as the address on the order.

• iOS 14.5 tracking changes

  In April 2021, iOS 14.5 introduced App Tracking Transparency, which forced apps to ask permission before tracking a user across other companies' apps and sites. Most people declined. For Meta advertisers the effect was not fewer sales but fewer sales Meta could see, which distorted every report built on them.

• First-party tracking

  First-party tracking means the shop collects visitor events on a domain it owns, such as a subdomain of its own shop, instead of sending them to a shared vendor domain. Blockers and browsers treat the two differently: a request to the shop's own domain is part of the site, not a third party.

• Event deduplication

  Event deduplication is how an ad platform recognises that two reports of the same sale, one from the shopper's browser and one from the shop's server, are the same event and must be counted once. The platform matches them on a shared identifier the shop sends with both.

• Meta Pixel

  The Meta Pixel is a small script a shop puts on its site so that Meta learns what visitors do there: pages viewed, carts started, purchases completed. It reports from the shopper's browser, which is both what makes it useful and what makes it lossy.

• ROAS

  ROAS, return on ad spend, is the revenue a campaign produced divided by what it cost to run. A ROAS of 3 means three units of revenue for every one spent. It is the number most shops steer on, and it is only as honest as the sales the platform managed to see.

• Attribution window

  An attribution window is the period after someone sees or clicks an ad during which a sale still gets credited to that ad. It is a reporting rule, not a fact about the shopper: the same sale can belong to one campaign under one window and to none under another.

• Hashed customer data

  Hashed customer data is the customer details attached to an event after they have been run through a one-way function, usually SHA-256, so the ad platform receives a fixed-length string rather than the email or phone number itself. The platform hashes its own records the same way and compares the two strings.

• Click ID

  A click ID is a parameter an ad platform appends to the link when someone clicks an ad, such as `fbclid` for Meta or `gclid` for Google Ads. It lets the platform recognise, when a sale is later reported, that the visit began with one of its own clicks.

• Ad blocker

  An ad blocker is software, usually a browser extension, that stops advertising and tracking scripts from loading or from sending anything back. For a shop it matters in one specific way: a blocked tracking script cannot report a sale, so the sale still happens but the ad platform never hears about it.

• Consent Mode

  Consent Mode is Google's mechanism for a site to tell its tags what a visitor agreed to, using a small set of named signals rather than simply removing the tags. The tags then adjust what they do: with consent they behave normally, without it they send less, or nothing.

• Device fingerprinting

  Device fingerprinting recognises a returning visitor by combining traits their browser exposes anyway, such as screen size, fonts, time zone and how their graphics stack draws a test image. Nothing is stored on the device, which is precisely why clearing cookies does not defeat it.