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What is a conversion API (CAPI)?

Quick Definition

A conversion API (CAPI) sends conversion events directly from your server to an ad platform's servers, bypassing the browser. Meta Conversions API, Google Enhanced Conversions, and TikTok Events API are the major implementations. Because the events travel server-to-server, CAPI keeps conversion tracking accurate even when browser cookies and pixels are blocked by Safari, iOS, and ad blockers.

How CAPI works

A pixel reports conversions from inside the user's browser. A conversion API reports the same conversions from your server. When a user converts — a purchase, signup, or lead — your backend (or your tracker) sends an event to the ad platform's API containing what happened plus identifying data the platform uses to match it back to the original ad click.

The major implementations, one per platform:

  • Meta Conversions API (CAPI) — the server-side counterpart to the Meta Pixel.
  • Google Enhanced Conversions — server-side conversion data for Google Ads.
  • TikTok Events API — server-side events for TikTok Ads.
  • Microsoft Offline Conversions and LinkedIn Conversions API — the same idea for those platforms.

Why CAPI became essential

Browser-only tracking has been breaking down since 2021: Safari's ITP caps cookies, iOS App Tracking Transparency blocks cross-app identifiers, ad blockers strip pixel scripts, and private modes drop cookies on close. The result is that a pixel-only setup now sees roughly 55–75% of actual conversions. CAPI recovers most of the missing events because the server has access to data the browser can't share — and isn't subject to the browser's blocking. This connects directly to server-to-server tracking and the broader shift toward first-party data.

Pixel and CAPI work together

CAPI doesn't replace the pixel — you run both. The pixel captures what it can from the browser; CAPI fills the gap from the server. To avoid double-counting, each conversion carries a shared event ID, and the ad platform deduplicates events that arrive from both sources. This redundant setup is now the standard for any serious paid-traffic operation.

Click IDs are what make CAPI accurate

CAPI's usefulness depends on match rate — how often the platform can tie your reported conversion back to the ad click that caused it. The strongest match signal is the click ID (fbclid, gclid, ttclid). Pass it with the event and match rates climb to 70–90%; omit it and you fall back to weaker signals (hashed email, phone, IP) that match at 20–40%. This is why preserving the click ID from landing page through to conversion is the make-or-break detail of a CAPI setup — covered step by step in the tracking-setup playbook.

Frequently asked questions

What is a conversion API (CAPI)?

A conversion API (CAPI) is a way of sending conversion events directly from your server to an ad platform's servers, bypassing the browser entirely. Instead of relying on a browser pixel that can be blocked, your server tells the ad platform "this user converted" along with identifying data. Meta Conversions API, Google Enhanced Conversions, and TikTok Events API are the main implementations. CAPI is how advertisers maintain accurate conversion tracking as cookies and pixels degrade.

Why do I need a conversion API?

Because browser-side tracking has been hemorrhaging conversions since 2021. Safari ITP, iOS App Tracking Transparency, ad blockers, and private browsing modes block or strip pixels, so a browser-only setup now sees roughly 55-75% of actual conversions. CAPI recovers most of the rest by sending events server-side, where the browser's restrictions don't apply. For paid traffic, running CAPI alongside the pixel is the difference between an ad algorithm that can optimize and one that's flying blind.

What's the difference between a pixel and a conversion API?

A pixel runs in the user's browser and reports events from there — easy to set up but blockable. A conversion API runs on your server and reports the same events server-to-server — harder to set up but reliable. They're complements, not alternatives: best practice is to run both with a shared event ID so the ad platform can deduplicate. The pixel catches what it can; CAPI fills the gap.

How do I improve CAPI match rates?

Pass as much identifying data as possible with each event — hashed email, hashed phone, IP, user agent, and especially the click ID (fbclid for Meta, gclid for Google, ttclid for TikTok). The click ID is the single strongest match signal; preserving it from the landing page through to the conversion payload typically lifts match rates from 20-40% to 70-90%. Clean, consistent event IDs for deduplication also matter.

Related terms

S2S Tracking

The broader server-to-server method

Click ID

What CAPI matches on

Postback URL

Network-to-tracker callback

Tracking Pixel

The browser-side counterpart

Put it to work

Wire CAPI into the full stack

CAPI is Layer 4 of the tracking stack. The playbook shows how it connects to UTMs, pixels, and postbacks — and how to preserve the click IDs that make it accurate.

Tracking Setup Playbook Tracking Software