What Is a Conversions API, and Why Marketers Need It Now

Attribution has always been the thorn in digital marketing's side—and today is no different. 

Growing privacy regulations and the ongoing demise of third-party cookies (despite Google changing its mind about phasing them out) mean that marketing teams face a looming challenge. According to a 2024 Statista survey, 92.8% of advertisers and publishers expressed at least some concern about the impact of third-party cookie deprecation on their business revenue, with 14.4% being very concerned.

Marketing teams need to figure out how to accurately track and measure campaign performance while adhering to privacy laws and user expectations.

This is where the conversions API (CAPI) comes in.

Conversions APIs transform how businesses capture and utilize customer interaction data in a privacy-first world. Read on to learn more about this increasingly valuable technology and how marketing teams can leverage it to make informed, data-driven decisions.

The conversions API gives marketers a comprehensive view of how their users and customers interact with their brands. This enables them to create more effective targeted campaigns based on user behavior across channels. And while web pixels are easier to implement in the short run, they are no longer able to provide as much useful insight while still respecting users' increasing desire for privacy. 

Conversions APIs, meanwhile, are changing the landscape in the following ways:

Conversions APIs offer a more reliable method of tracking customer interactions by collecting data server-side, ensuring you can collect critical data for optimizing campaigns, even if you encounter ad blockers or cookie limitations. They can receive data from both online and offline events, and are better at cross-device tracking. As such, they offer a more reliable view of the customer, while respecting their browser-based privacy controls. 

Because you own the data sent to ad platforms, you can choose which user activity and behavioral data you share. This means you can optimize ad spend for custom audiences at a more granular level.

Data privacy is an increasingly important topic. With more control, conversions APIs allow marketers to maintain compliance by managing data on their own servers, and not relying on third-party cookies. This also makes marketing teams more resilient against changes in data privacy regulations.

Conversions APIs capture customer behavior data across both online and offline channels. This enables marketers to have a more comprehensive understanding of how customers interact with their organization’s website or platform at various stages of the journey. It also supports teams in their efforts to provide more personalized experiences, which customers are increasingly demanding. 

With more precise data on how ads affect conversions, a conversions API improves campaign performance by feeding accurate data back into ad platforms. This helps marketers optimize targeting and retargeting efforts and reduce wasted ad spend.

As browsers like Safari and Firefox implement stricter privacy policies (e.g., blocking third-party cookies), conversions APIs ensure marketers can still understand how ads affect conversions and optimize campaigns based on data.

A conversions API sends real-time customer data such as purchase events or form fills, from a company's servers to ad platforms like Meta, TikTok, and Google Ads, ensuring accurate and secure tracking.

Traditional methods, such as Pixels or in-app SDKs, collect data from a user's activity within a browser. Data collection is often hindered by ad blockers or browser restrictions. The conversions API bypasses these limitations by tracking web events (and offline events) server side to provide more accurate tracking while respecting the user's privacy. This makes it easier to more accurately track events that lead to conversions.

Conversions APIs track a wide range of events, including: 

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

In addition, some conversions APIs (e.g., Meta) support offline customer events, such as in-store purchases or orders made over the phone.

Major ad platforms like Meta, Google, Twitter, TikTok, Pinterest, Snapchat, and Reddit have built APIs that allow websites to feed conversion data directly to their systems. 

Conversions APIs directly transmit event data from a server-side environment to advertising platforms.

Here's what that looks like in practice:

Event tracking and data transmission: Any time a customer takes an action, such as filling out a form or making a purchase, that data is captured by your customer data platform (CDP) or another server-side data collection method. The CDP securely forwards this data via the conversions API to the corresponding ad platform, ensuring seamless server-to-server transmission.

Server-side integration: The conversions API bypasses traditional tracking challenges like cookie restrictions and ad blockers by sending data directly from the server to the ad platform using secure protocols. For example, when a customer makes an online purchase, the retailer's CDP can send their email address and name directly to the ad platform's backend through a secured request.

Data transmission protocol: Data is sent via secure methods, like HTTPS, ensuring privacy and integrity. Before the conversions API receives the data, it checks to make sure the source is legitimate. It's like having a secure, private channel for sending information. 

Authentication: To ensure the security of the connection and data transfer, an authentication mechanism is designed to ensure that the data is coming from a trusted source.

Error handling: Conversions APIs are set up to flag if data has not been received correctly or if any issues need to be remedied.

Matching events to users: Conversions APIs use secure methods such as hashing identifiers, like email addresses, phone numbers, or unique IDs to link conversion events to specific users, while maintaining privacy compliance. In other words, conversions APIs will keep personally identifiable information (PII) safe while linking actions to specific accounts or users.

Campaign attribution: Conversions APIs are able to track which ads lead to conversions, offering deeper insights into performance, and allowing marketing leaders to make informed decisions about where to spend their ad dollars. 

Web pixels and conversions APIs both serve as tools for tracking user behavior, but they differ significantly in the type of data they can access.

Web pixels are client-side—they operate within the user's browser—and typically capture and share third-party data that isn't owned by you. Their reliance on client-side tracking and third-party cookies limits their reliability in today’s privacy-first landscape. In the case of Facebook Pixel, for example, Facebook collects and sends the data. With that being said, they can sometimes also work with first-party cookies.

The problem is that they can only capture browser events and website interactions, such as a click or a purchase. Ultimately, heightened privacy regulations, cookie restrictions in Safari and Firefox, and iOS 14+ policies that allow users to prevent tracking make web pixels less effective. 

On the other hand, a conversions API operates on the server-side. As a server-side tool, they bypass the limitations of third-party cookies and browser preferences by collecting data directly from your website or application's internal servers. This approach also gives you added flexibility and reliability because you own all the conversion data. 

Conversions APIs serve a large number of industries and use cases: 

• Lead generation: Track user interactions, such as form submissions or call-to-action clicks, even if the user’s browser doesn’t support traditional tracking.
• eCommerce: Monitor events like purchases, product views, or cart abandonment with more accuracy, ensuring any retargeting strategies are based on complete data.
• Mobile apps: Capture install attribution, in-app events, and cross-platform user journeys.
• B2B lead tracking: Measure form submissions, content downloads, and account creations alongside CRM updates.
• Offline events: Capture offline actions like in-store purchases, call center interactions, or CRM updates and integrate these into the broader digital marketing strategy.
• Travel companies: Track booking events, cancellations, and customer preferences across web, mobile, and call centers for personalized promotions.

While conversions APIs are highly effective, implementing them requires careful planning and an investment in resources. That said, the return on investment is worth it. Here’s what you need to make the most of your efforts:

Building a conversions API isn’t a simple task. It requires technical knowledge, API linking, and a corresponding build for each platform. Plus, you need to keep up with changes in each platform. Ad platforms such as Meta and TikTok constantly enhance their APIs, which requires ongoing maintenance on your end.

When collecting data from sources like CRMs or apps, it's essential to connect them in a centralized location. Leveraging a customer data platform like mParticle can make integrating your various data sources easier and enable you to have a single source of truth for your customer data.

Having the right people on your team ensures you're making the most out of your conversions APIs. Hire data engineers and data analysts—and ask for support from data governance specialists. 

In an increasingly privacy-focused digital ecosystem, conversions APIs represent the next generation of customer data measurement solutions. They offer a privacy-conscious approach to tracking that doesn't compromise on insights or accuracy. 

Marketing leaders who adopt this technology now will build sustainable measurement frameworks. They can meet customers where they are, balancing personalization with privacy, and make stronger, data-driven decisions about spend.

To learn more about how you can leverage customer data to make your offerings more impactful and how mParticle’s pre-built Conversions API integrations can help you navigate this privacy-first era, read our guide to customer data platforms.