Conversions API vs Pixel: what's actually different and which you need

Half of Shopify operator conversations about CAPI start with the wrong frame: should I use Pixel OR Conversions API? The answer is both. They're complementary, not alternative. Here's what each actually does.

What the Pixel does

The Pixel is JavaScript that runs in the visitor's browser. It captures the visitor's interaction with your site (page views, add-to-carts, purchases) and sends events to Meta along with browser-level identifiers (fbp cookie, fbc cookie, IP address). Meta uses those identifiers to match the event to a user in their graph.

Strengths: catches view-through conversions, captures behavior on iOS visitors who haven't opted into tracking, ties to ad clicks via fbc.

Weaknesses: subject to iOS 14.5 cookie restrictions, blocked by ad blockers (about 25% of visitors), can't see post-purchase events that happen off-site.

What Conversions API does

CAPI is a server-to-server API. Your server sends events directly to Meta's API with customer-level identifiers (hashed email, phone, name, address). Meta matches on those identifiers instead of browser cookies.

Strengths: bypasses ad blockers and iOS cookie restrictions entirely, can fire post-purchase events (shipped, refunded) that the Pixel can't see, customer-parameter coverage drives match rate higher.

Weaknesses: no view-through tracking (the user has to actually convert, not just see the ad), can't capture intermediate behaviors like page views, requires customer-parameter coverage to match correctly.

Why you need both

Pixel captures the upper-funnel signal Meta needs for prospecting optimization. CAPI captures the post-purchase signal Meta needs for accurate ROAS reporting. Together with event_id deduplication, Meta dedupes them into a unified event stream that's more complete than either alone.

If you only run Pixel: you lose 20-30% of attribution on iOS. If you only run CAPI: you lose view-through tracking and prospecting signal. Both together: closest to ground truth.

How to install both on Shopify

Shopify's free Meta channel app does both for you. Pixel installation, CAPI setup, event_id deduplication, Automatic Advanced Matching. It's the cleanest path. Custom implementations work but require getting deduplication right manually, which is where most Shopify CAPI setups fail.