Measurement · also called CAPI, server-side tracking, server-to-server conversions
Conversions API (server-side tracking)
A conversions API sends conversion events, such as purchases or sign-ups, directly from an advertiser's server to an ad platform, instead of relying only on browser pixels.
Traditionally, a tracking pixel in the browser told an ad platform when someone bought something. Ad blockers, browser tracking protections, cookie limits and consent choices mean many of those signals now go missing. Server-side tracking sends the event from the advertiser's own server to the platform's API instead.
Examples include Meta's Conversions API, Google's enhanced conversions and offline conversion uploads, TikTok's Events API and similar tools from Snap, Pinterest, LinkedIn and retail media networks. Events usually include a timestamp, value and identifiers such as a click ID or a hashed email, which the platform matches to its users.
The benefits are more complete and reliable measurement and more control over what data is shared. The responsibilities are real, though: advertisers must honour consent (for example via CMPs and Google's consent mode), follow data minimization and avoid sending PII that has not been properly hashed or permitted. Server-to-server events can also be faked, so platforms deduplicate and validate them.
Think of it like this
Pixels are like asking a shop's customers to phone in their receipts; a conversions API is the shop sending the receipts itself.
An example
An online furniture retailer in the UK adds Meta's Conversions API alongside its pixel and sees the share of purchases matched to ads rise from 70% to 88%, after deduplicating events recorded by both.
Related terms
Tracking pixel
A tracking pixel is a tiny piece of code, historically an invisible 1x1 image, that loads when a page or ad is viewed and reports that event to a server.
Hashed email
A hashed email is an email address transformed by a one-way cryptographic function, usually SHA-256, into a fixed string used to match users across systems without sharing the plain address.
First-party data
First-party data is information a company collects directly from its own customers or audience, such as purchases, sign-ups, app use and site behaviour, through its own channels.
Signal loss
Signal loss is the reduction in data available to target, measure and optimise advertising, caused by browser cookie blocking, mobile ID restrictions, privacy laws, consent choices and ad blocking.
Attribution
Attribution is the process of assigning credit for a conversion, such as a sale, sign-up or install, to the ads, channels or touchpoints that a customer encountered beforehand.
Sources: Meta for Developers: Conversions API, Google Ads API: upload click conversions, Google Tag Platform: consent mode