What exactly are conversion APIs?

Published May 23 2023 Last updated Feb 26 2024 7 minute read
conversion apis
  • Sean Dougherty
    Written by Sean Dougherty

    A copywriter at Funnel, Sean has more than 15 years of experience working in branding and advertising (both agency and client side). He's also a professional voice actor.

In the world of performance marketing, data sits at the head of the table. Tracking user interactions and conversions is critical for optimizing campaigns and maximizing your return on investment (ROI), and this is where the conversion API (application programming interface) comes into play. These applications serve as the connective tissue between marketing platforms and user data, providing real-time, reliable information that helps marketing professionals make accurate, data-driven decisions.

As digital channels continue to expand and personalization further integrates into marketing strategies, conversion APIs become more crucial. They give marketers a comprehensive picture of their audience and help them create effective, targeted campaigns based on user behavior across various channels.

It’s clear that conversion APIs play a critical role in performance marketing and ad campaigns. Since you’re here — hello, you! — you’re likely seeking answers to questions like:

  • What are conversion APIs?
  • What’s the difference between conversion APIs and pixels?
  • Why should conversion APIs be used?

Let’s dive in.


What are conversion APIs?

A conversion API, or server-side API, allows you to send events directly from your server to third-party advertising platforms. Unlike a web pixel, which is client-side, conversion APIs give added flexibility and reliability since you own all of the conversion data. 

As a server-side tool, a conversion API is not limited by third-party cookies or browser settings, because all the collected data comes from internal servers running your website or application. This makes these APIs especially attractive due to the limits on tracking software, the disappearance of third-party cookies for iOS users, and the increasing relevance of strict privacy laws.  

These privacy changes have rendered client-side event tracking (web pixels) less effective, prompting a shift toward server-side tracking methods. As a result, major players such as Twitter, Pinterest, TikTok, Spotify, and Facebook, which previously relied on the Facebook Pixel, have adopted server-side tracking methods like conversion APIs in response.

Conversion APIs: An example

Still unclear about what is a conversion API? Not to worry. You might think of it as a private courier service that picks up packages (data) directly from your warehouse (server) and delivers them to a recipient (third-party advertising platforms). You have complete control over the packages you send, and you own all the contents inside. This private service is not affected by traffic laws (third-party cookies), road conditions (browser settings), or detours (ad blockers) because it relies on its private road system (internal servers).

Web pixels, such as the Facebook Pixel, are like the regular postal service. They send packages, but less reliably, and their dependence on public roads means they are affected by traffic laws, road conditions, and detours. And while you can have the service deliver packages on your behalf, you lose control of the items once you hand them over.

Recommended reading: The benefits of server-side tagging


Conversion APIs and web events tracking

A conversion API can track various web events. The types of events will depend on which digital advertiser you’re working with, but some of the common ones include:

  • Site visits
  • Completed purchases
  • Content downloads
  • Webform fills 
  • Custom actions

The benefits of using a conversion API

Here are five key benefits of using conversion APIs:

1. Improved advertising performance 

By capturing CRM data, server events, conversion data, and other web activities, the platform’s algorithm can track ad performance and optimize accordingly, leading to improved metrics like ROAS (return on ad spend). This is especially valuable if you work with advanced AI-based platforms like Google Performance Max and Meta Advantage+.

2. Increased control and flexibility

Since you own the data sent to ad platforms, you can choose the specific user activity and behavioral data you share, allowing you to optimize ad spend for custom audiences at a granular level.

3. Resilience against changes in data privacy 

Third-party cookies are disappearing, and tracking is becoming more tightly regulated around the world. Since conversion APIs are built for first-party data collection, they are less affected by data privacy laws and other online blockers.

4. More effective advertising performance

Building conversion APIs requires coordination, proper linking to the API, and conversion API builds for each relevant advertising platform. Even though there are necessary development and maintenance costs, the rewards of more effective advertising performance far outweigh these expenses.

5. Improved customer journey tracking

Since conversion APIs capture detailed behavioral data (like views, clicks, and purchases), you get a better look into your customer’s ideal customer journey. When you have a better idea of how your customers interact with the website or platform, you’ll produce a more effective and personalized experience. It’s almost like a cheat code, but not quite.

Recommended reading: How do APIs work


Downsides of using conversion APIs

Of course, there are potential downsides to conversion APIs like Facebook Conversions API. The main downside is the amount of time-consuming technical tasks required.

Building conversion APIs isn’t as simple as dropping a pixel on your website. Instead, they require technical knowledge, API linking, and a corresponding build for each platform.

Chances are that, on top of web events, you’re also tracking customer data points from other systems your company uses, such as:

  • CRM data (like lead events)
  • Purchase events
  • App data

For each system you use to collect customer information, make sure it’s connected correctly and able to transmit data accurately.

Connecting multiple solutions to transmit data comes with increased development costs and added maintenance time and effort. It’s not a one-and-done approach; instead, it’s a continuous process that requires ongoing attention. 

Still sounds too complex? Keep reading, and you’ll understand all the ins and outs in no time. We believe that using conversion APIs for more effective advertising performance outweighs the technical burden and costs.

Many major digital advertising platforms are incorporating conversion APIs, making it evident that this level of ad optimization and tracking is essential to maximize ROI. 

Recommended reading: The future of performance marketing - Part 1

Let’s now turn to how the Facebook Pixel and Facebook Conversion API tools compare.


Facebook Pixel tracking vs. Facebook Conversions API

The Facebook Pixel (or Meta Pixel) and the Facebook Conversions API track online customer web activity, which feeds into the Facebook ads manager. The difference between them lies in how Facebook collects the data.

Facebook Pixel

The Facebook Pixel uses browser-side tracking, known as client-side tracking, which relies on cookies to gather online conversion events from website visitors. The two main limiting factors of client-side tracking are:

  1. It can only capture browser events and website interactions.
  2. Ad blockers, cookie blockers, and ongoing privacy laws limit the effectiveness of client-side tracking tools like Facebook Pixel.

You do not own the data created because the pixel owner collects and sends the data. In this case, it’s the Facebook Pixel, but this fact holds with other web pixels.

Facebook Conversions APIs

The Facebook Conversions API, like other conversion APIs, uses server-side conversion tracking to send web events. This means that all data tracked lives on your server. You own the data created, which is referred to as first-party data.

A user’s browser settings, ad blockers, third-party data, third-party tools, and cookies aren’t as limiting with Facebook Conversions API as with the Facebook Pixel. 

Let’s see an example:

Think of the Facebook Pixel as a tour guide. This guide can tell you everything happening on the tour, but only within the tour’s boundaries (client-side tracking). They can’t report anything beyond that. 

  • Some tourists may ignore the guide completely (like using ad blockers). 
  • Laws might restrict where the guide can take the group, limiting the information the guide can gather. 
  • The guide’s notes about the tour belong to the tour company rather than the tourists themselves.

On the other hand, the Facebook Conversions API works like a travel journal. It contains all of the details of the each tourist’s trip — both those with the guide and those off the official tour. That is, it combines the platform’s client-side tracking as well as the events on your own website or app (server-side tracking).

  • This method is more comprehensive and less likely to miss information because it’s not dependent on a single guide. 
  • The notes in the journal belong to you, not the tour company (first-party data).

When tracking data, most conversion APIs work the same way Facebook Conversions API does. The difference lies in the types of data you’re able to send.


Which other companies offer a conversion API?

In addition to Facebook, companies like Twitter, TikTok, Pinterest, and even Spotify provide conversion APIs for sending website data back to their platforms.

Here’s a brief introduction to each platform’s conversion API to help you get started.


The Facebook Conversions API plays a significant role in how the company tracks data and optimizes custom audiences for improved ad delivery. 

What happens if you’re already using the Facebook Pixel? Don’t worry. You can set up the Facebook Conversions API and Facebook Pixel set, since Facebook can remove duplicate conversion events.

To get started, head to Facebook’s help center for a walkthrough on setting up their Conversions API for Facebook advertising and conversion data collection.


Twitter Ads conversion tracking allows you to measure Twitter users’ actions once they interact with one of your ads.

To get started with Twitter’s conversion tracking, you’ll need to create a developer account if you don’t have one. We recommend reviewing Twitter’s conversion API setup documentation for a detailed step-by-step guide.


Pinterest doesn’t have a separate conversion API. Instead, conversions are tracked using the Pinterest API. Implementing conversions requires a different code from developers, making it different from shopping and other API use cases.

You can send data via web, in-app, and offline conversions to Pinterest’s server. Pinterest categorizes events received in real time or within an hour of the event as web or app events. Batch events and anything received outside that window earn the offline events classification. 

Check out Pinterest’s help center to learn more about the setup process to implement Pinterest’s API for conversions.


TikTok’s Events API is what the publisher uses to enable conversion tracking. They recommend combining their Pixel and Events API to optimize ad delivery.

TikTok offers several ways to integrate the events manager:

  • Commerce partner integration: For advertisers who work with one of TikTok’s commerce partners.
  • Data partner integration: For advertisers who partner with one of TikTok’s data partners.
  • Direct integration: For advertisers who prefer complete control over their data and have the technical resources.

Visit TikTok’s help guide to learn everything you need to know about implementing their Events API and Pixel. 

Recommended reading: A US Tiktok ban? What should advertisers do?


If you’re not yet sold on the popularity and benefits of conversion APIs, pause your music and check this out. 

The Spotify Ads API lets you build, manage, and report on Ad Studio campaigns. Basic reporting is available to all advertisers, but their Campaign Management capabilities are still in development as a closed beta. If you want to gain access to the closed beta, you’ll need to submit a request to the Spotify Ads API team.

Learn more about the Spotify Conversions API by visiting their developer documentation.

What’s next?

Conversion APIs are powerful tools for improving your advertising efforts at a granular level due to the amount of data you can collect. This is especially helpful considering the global crackdowns on privacy and tracking.

There is no doubt that building and maintaining conversion APIs will be time-consuming and technical, but it’s worthwhile to implement them.

Think of it this way: opting for conversion APIs over pixel-based tracking is like choosing to plant an oak seedling versus a pre-grown bonsai tree. Of course, the oak seedling requires more work, but the payoff is exponentially greater in the long run.

You might not be an arborist, but in digital marketing, conversion APIs are reshaping how we understand and engage with our audience. So, plant your oak seedling today and reap the rewards of an eventual mighty oak tree.

Frequently asked questions

How do conversion APIs integrate with privacy regulations such as GDPR and CCPA?

Conversion APIs are designed to align with privacy regulations by securing user data and ensuring consent is obtained where necessary. Features for data anonymization and secure transmission are typically included to aid compliance.

What are the technical requirements for businesses to use conversion APIs?

A basic technical setup, including a website or app, is necessary. Technical expertise is needed for API integration and to manage secure data transmission.

Can conversion APIs be integrated with other marketing technologies or platforms?

Yes, conversion APIs can enhance data accuracy and real-time reporting by integrating with various marketing technologies, improving targeting and measurement across digital marketing campaigns.

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