Glossary
Conversion API (CAPI)
A method of sending conversion and event data directly from a business's own servers to an ad platform, bypassing the browser.
Also called: CAPI, server-side conversion tracking
A conversion API sends event and conversion data from an advertiser's own servers directly to an ad platform, rather than relying solely on a browser-based pixel that fires from the user's device. Because the data travels server-to-server, it does not depend on a script loading successfully in the browser and is less affected by ad blockers, browser tracking restrictions, or a user closing the tab before a pixel fires.
Conversion APIs are usually run alongside, not instead of, browser-side pixel tracking, and platforms deduplicate the two using a shared Click ID or event identifier so the same conversion is not double-counted. This server-side approach is part of the broader shift toward cookieless tracking and server-side tagging, as browsers phase out support for third-party cookies and restrict how much tracking scripts running in the browser can see.
Conversion APIs matter because they recover conversion signal that browser-only tracking increasingly misses, which directly improves the data available to data-driven attribution and campaign optimization. Implementing one correctly requires care: sending inconsistent or duplicate events, or using mismatched identifiers between browser and server events, produces conversion counts that look plausible but are actually wrong.
Last reviewed September 22, 2026