Glossary/Ad Tech & Ecosystem/Conversion API (CAPI)
Ad Tech & Ecosystem

Conversion API (CAPI)

Also known as: CAPI, Conversions API

Server-to-server API for sending conversion events to Meta (and other platforms).

Conversion API (CAPI) is a ad tech & ecosystem concept that ecommerce teams touch every week, usually without agreeing on a definition first. This page sets out what it means, how to apply it at catalog scale, what to measure, and where it breaks.

Definition

CAPI lets your server send conversion events directly to Meta, complementing (and increasingly replacing) client-side pixel events. Deduplication ties CAPI + pixel together into one event.

Why it matters

Client-side signal has degraded (iOS ATT, browser blockers). CAPI reclaims that signal by measuring server-side, which the browser can't intercept.

User buys
Pixel fires (browser)
Server fires (CAPI)
Meta dedupes by event_id
One counted conversion

Conversion API (CAPI) in practice

CAPI lets your server send conversion events directly to Meta, complementing (and increasingly replacing) client-side pixel events. Deduplication ties CAPI + pixel together into one event. Ad-tech components are the plumbing between an impression, a bid and a recorded conversion. You rarely touch them directly day to day, but when they are misconfigured every downstream number is wrong — and the symptom looks like a creative or targeting problem. Read it next to Meta Pixel, Attribution, First-Party Data.

How to get it right

Document the data path end to end: what fires, where it is sent, what identifiers travel with it and what consent state applies. Prefer server-side event delivery for durability, dedupe events explicitly, and re-verify after any site or checkout change.

What to measure and watch

Validate rather than assume. Compare event counts against orders in your commerce system, check event match quality where the platform exposes it, and watch for silent drops after releases. A five percent signal loss is invisible in a dashboard and material in delivery. Why this matters commercially: Client-side signal has degraded (iOS ATT, browser blockers). CAPI reclaims that signal by measuring server-side, which the browser can't intercept.

Where Conversion API (CAPI) sits in an agentic creative workflow

Clean signal is what lets an automated creative loop work at all: Xeli attributes results back to concepts and SKUs, and that mapping is only as good as the events underneath it. Fix the plumbing first, then let the loop compound. In the context of ad tech & ecosystem, that means the concept stops being something a person re-applies by hand every campaign and becomes a rule the system enforces on every asset it produces.

Frequently asked questions

CAPI lets your server send conversion events directly to Meta, complementing (and increasingly replacing) client-side pixel events. Deduplication ties CAPI + pixel together into one event.

Client-side signal has degraded (iOS ATT, browser blockers). CAPI reclaims that signal by measuring server-side, which the browser can't intercept.

Even single-channel accounts depend on this layer for measurement quality. At minimum, verify events are firing once, matching well and surviving consent — see conversion-api for the durable server-side path.

Closely connected concepts include Meta Pixel, Attribution, First-Party Data.