A Conversions API (often shortened to CAPI) is a general idea: send conversions to an ad platform directly from the server, not just from the browser via a pixel. Under various names, most major platforms now offer one.
How it differs from the pixel
The pixel is a piece of JavaScript that runs in the browser and sends events to the platform from there. A Conversions API sends the same events server-to-server from your server. The pixel has richer browser data but is blocked by ad-blockers and limited by ITP; a Conversions API is more reliable because it doesn't depend on the browser.
Why Conversions APIs exist
As ad-blockers, Safari ITP and iOS reduced pixel accuracy, platforms needed a way to receive conversions reliably. A Conversions API is the answer — and the recommended practice today is to run the pixel and CAPI together with deduplication.
Which platforms have one
- Meta — Conversions API (for Facebook and Instagram).
- TikTok — Events API.
- Pinterest — Conversions API.
- Google — the Measurement Protocol (GA4) and server-side conversion uploads to Google Ads serve a similar purpose.
- Other platforms have similar server-to-server interfaces too (Snapchat, Reddit, LinkedIn and more).
What they have in common
- Events are sent server-to-server, often with hashed identifiers for better matching.
- They require deduplication with the pixel (via an event ID) so conversions aren't counted twice.
- They process personal data, so they need consent and correct handling under GDPR.
For an in-depth example, see the Meta Conversions API guide. Server-side GTM is the tool that connects these interfaces from one place — see the complete guide to server-side tracking.