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Web vs. App Tracking in GA4: Key Differences, Tools & Best Practices
Learn the key differences between web and app tracking in GA4. Explore best practices, tools like GTM and Firebase SDK, and how to ensure data consistency across platforms. Improve cross-device tracking and make smarter marketing decisions.
Ricardo Cristofolini
Senior Implementation Specialist, Data Solutions
I’m passionate about what I do. If you meet my manager or co-workers, they would say I’m a team player, engaged and always excited to learn something new. Like everyone else I have some flaws. However I’m not afraid to work around those to bring the best in myself and for the company
It’s 2025. We are living and breathing technology. Every day, we get new emails, marketing ads, articles, social media posts, and everything in between that the internet can provide, so we are - or trying to - be up to date with everything. But that does not happen out of thin air, and even though some people may say that it’s automatic, there’s always a human hand behind it.
To do that, those little humans have to have reliable data being collected from websites and/or apps. In other words, accurate data tracking is essential for businesses to make informed decisions, optimize marketing strategies, and understand user behaviour across web and mobile platforms.
That then happens in two locations: Web and App.
Whether on a website or within an app, tracking allows organizations to target the right audience, improve user experience, and drive conversions.
However, since we are dealing with two different environments, collecting data is not the same and - sometimes - not as straightforward as we would like. The implementation of tracking differs significantly between web and app environments, requiring tailored approaches and tools.
It’s also important to note that consistency between App and Web implementation is extremely important for cross-device tracking. That scenario is most common in companies that have both implementations in place. For example, a user checks your products on your website and ends up making a purchase using the App. If you have different events for the same behaviour (e.g. login in the web vs user_login in the App), you will have a duplication of events for the same action, which can give you a hard time with business decisions and tracking understanding.
This article explores the key differences, best practices, and necessary tools for tracking across both platforms.
How Web Tracking Works
Using a Tag Manager
For websites, tracking implementation is often handled through a tag management system like Google Tag Manager (GTM). GTM allows for event tracking, pixel placement, and analytics integration without requiring direct code changes in the site's source files.
Other tag managers include:
Tealium
Adobe Launch
Ensighten
The one you use depends on your setup and what your business needs.
You’ll Still Need a Developer
While tools like GTM simplify tracking, installing the tag manager on your website, and building the infrastructure to work with it, will require development experience to build a data layer to support it, scrape values from the page, or build event listeners to bind tags to. Of all of that, the most important is the Data Layer since the main reason for this is the data tracking best practices. By having a Data Layer implemented, data flows logically and more straightforwardly:
Here’s how it works:
The website loads
The data layer loads
GTM loads
The data is sent to GA4 or another platform
In other words, the Data Layer is a custom JavaScript that holds all the information about a specific user interaction on your site or general information about a page (non-interaction data).
Event Listeners vs. Data Layer
Tracking on the web can be implemented using event listeners that directly trigger tags in GTM. Now, Event Listeners are not directly connected to the Developers, but it will require some developers’ work regarding web dev. The reason is that, in GTM, when we use Event Listeners instead of Data Layer events, we look for, mostly, Classes and IDs. If a page is missing that, it makes it difficult to trigger tags in GTM.
Keep in mind that this method is not recommended as it can become difficult to manage at scale. Instead, a Data Layer approach is preferred, where event data is structured and pushed into a standardized format, making tracking more robust and maintainable.
The Data Layer acts as an intermediary between the website and GTM, holding structured data that can be used by multiple tracking tools. Implementing a well-structured data layer ensures that tracking remains consistent and scalable, reducing the reliance on direct DOM-based event tracking.
In other words, using the Data Layer provides better data implementation, tracking, and consistency, and follows best practices.
How App Tracking Works
Installing an SDK
Unlike web tracking, app tracking requires the installation of an SDK, such as the Firebase SDK, to enable GA4 tracking. SDKs handle data transmission, session management, and offline tracking capabilities that are not easily achievable through traditional tag managers. However, this simple installation is not enough because the SDK does not know what you want to track. It’s a simple “translator” to send the data to GA4. That means you still have to customize the code in the SDK to send the events you want to track. It’s like the Data Layer and GTM together, but when dealing with Apps, the data gets sent directly to GA4.
Do You Need GTM for Apps?
In most cases, you don’t need to use GTM with your app. Here’s why:
The SDK custom code implemented for tracking IS the actual Data Layer
The GTM container for Apps does not have as many functionalities as the Web one, so you will end up with fewer options to do your App tracking
Avoid code bloat since adding GTM can turn into an unnecessarily long, slog or wasteful of resources due to redundant or poorly optimized code
With the GA4 introduction, many things done in the App GTM Container can now be done in GA4s Add or Modify events or event GTM server-side request modification
Unless there’s a special reason, it’s usually better to skip GTM for apps.
Testing Your Setup
When it comes to testing, GA4 has the Debug View that allows you to see the data flowing into GA4 from both the Web and App. However, different on the Web, testing Apps can be more difficult due to several steps required.
Testing Web Tracking
To test your website tracking, you’ll need:
Access to GTM (to preview and publish changes)
Access to the website (to check if tags are firing)
Access to GA4 (to see if data is coming through)
Extra tools like Analytics Debugger or Omnibug can help you check that everything is working the way it should.
Testing App Tracking
Testing Apps will depend on the type of implementation done. You may need all - or some - of the accesses below:
1. Developer Tools
Android Studio for Android
Xcode for iOS
Testing platforms like Firebase App Distribution or TestFlight
Installation of Android Studio and Xcode for testing app tracking implementations in simulated or real environments. Keep in mind that if you have a Windows computer, testing with Xcode (iOS) can be more complicated than it seems. This approach also includes the requirements for testing platforms in some cases such as Firebase App Distribution, Beta, or Test Flight. All of those fall into the Physical devices option mentioned below.
2. App Files
You’ll need the app file: APK for Android or IPA for iOS
APKs won’t run on iPhones, and IPAs won’t run on Androids, so you’ll need both types of devices or tools
Access to compiled versions of the app (APK for Android, IPA for iOS) to test tracking without relying on production releases. The same goes for the computer you have on hand. APK will only run on Android and IPA on iOS which means, at least, two computers if you don’t want to have hacky solutions.
3. Physical Devices
Testing should cover both iOS and Android devices to verify event tracking consistency across different platforms. This can be an issue if you have multiple team members in different locations who are required to test the App. For this, you may be able to use virtual devices in multiple testing platforms online but none of them - as of the time of this writing - support the level of information required to test GA4 events.
You can also use apps like Charles Proxy, Proxyman, or HTTP Toolkit to see exactly what data your app is sending.
Conclusion
Tracking users on websites and apps is important, but the process is very different. Websites use tools like GTM and data layers to organize and send data. Apps need SDKs and custom code to do the same job.
To get the best results, you need the right setup and tools for each platform. And don’t forget to test! Good tracking helps you make better decisions and understand your customers more clearly—no matter where they are.
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Web vs. App Tracking in GA4: Key Differences, Tools & Best Practices
Learn the key differences between web and app tracking in GA4. Explore best practices, tools like GTM and Firebase SDK, and how to ensure data consistency across platforms. Improve cross-device tracking and make smarter marketing decisions.
Ricardo Cristofolini
Senior Implementation Specialist, Data Solutions
I’m passionate about what I do. If you meet my manager or co-workers, they would say I’m a team player, engaged and always excited to learn something new. Like everyone else I have some flaws. However I’m not afraid to work around those to bring the best in myself and for the company
It’s 2025. We are living and breathing technology. Every day, we get new emails, marketing ads, articles, social media posts, and everything in between that the internet can provide, so we are - or trying to - be up to date with everything. But that does not happen out of thin air, and even though some people may say that it’s automatic, there’s always a human hand behind it.
To do that, those little humans have to have reliable data being collected from websites and/or apps. In other words, accurate data tracking is essential for businesses to make informed decisions, optimize marketing strategies, and understand user behaviour across web and mobile platforms.
That then happens in two locations: Web and App.
Whether on a website or within an app, tracking allows organizations to target the right audience, improve user experience, and drive conversions.
However, since we are dealing with two different environments, collecting data is not the same and - sometimes - not as straightforward as we would like. The implementation of tracking differs significantly between web and app environments, requiring tailored approaches and tools.
It’s also important to note that consistency between App and Web implementation is extremely important for cross-device tracking. That scenario is most common in companies that have both implementations in place. For example, a user checks your products on your website and ends up making a purchase using the App. If you have different events for the same behaviour (e.g. login in the web vs user_login in the App), you will have a duplication of events for the same action, which can give you a hard time with business decisions and tracking understanding.
This article explores the key differences, best practices, and necessary tools for tracking across both platforms.
How Web Tracking Works
Using a Tag Manager
For websites, tracking implementation is often handled through a tag management system like Google Tag Manager (GTM). GTM allows for event tracking, pixel placement, and analytics integration without requiring direct code changes in the site's source files.
Other tag managers include:
Tealium
Adobe Launch
Ensighten
The one you use depends on your setup and what your business needs.
You’ll Still Need a Developer
While tools like GTM simplify tracking, installing the tag manager on your website, and building the infrastructure to work with it, will require development experience to build a data layer to support it, scrape values from the page, or build event listeners to bind tags to. Of all of that, the most important is the Data Layer since the main reason for this is the data tracking best practices. By having a Data Layer implemented, data flows logically and more straightforwardly:
Here’s how it works:
The website loads
The data layer loads
GTM loads
The data is sent to GA4 or another platform
In other words, the Data Layer is a custom JavaScript that holds all the information about a specific user interaction on your site or general information about a page (non-interaction data).
Event Listeners vs. Data Layer
Tracking on the web can be implemented using event listeners that directly trigger tags in GTM. Now, Event Listeners are not directly connected to the Developers, but it will require some developers’ work regarding web dev. The reason is that, in GTM, when we use Event Listeners instead of Data Layer events, we look for, mostly, Classes and IDs. If a page is missing that, it makes it difficult to trigger tags in GTM.
Keep in mind that this method is not recommended as it can become difficult to manage at scale. Instead, a Data Layer approach is preferred, where event data is structured and pushed into a standardized format, making tracking more robust and maintainable.
The Data Layer acts as an intermediary between the website and GTM, holding structured data that can be used by multiple tracking tools. Implementing a well-structured data layer ensures that tracking remains consistent and scalable, reducing the reliance on direct DOM-based event tracking.
In other words, using the Data Layer provides better data implementation, tracking, and consistency, and follows best practices.
How App Tracking Works
Installing an SDK
Unlike web tracking, app tracking requires the installation of an SDK, such as the Firebase SDK, to enable GA4 tracking. SDKs handle data transmission, session management, and offline tracking capabilities that are not easily achievable through traditional tag managers. However, this simple installation is not enough because the SDK does not know what you want to track. It’s a simple “translator” to send the data to GA4. That means you still have to customize the code in the SDK to send the events you want to track. It’s like the Data Layer and GTM together, but when dealing with Apps, the data gets sent directly to GA4.
Do You Need GTM for Apps?
In most cases, you don’t need to use GTM with your app. Here’s why:
The SDK custom code implemented for tracking IS the actual Data Layer
The GTM container for Apps does not have as many functionalities as the Web one, so you will end up with fewer options to do your App tracking
Avoid code bloat since adding GTM can turn into an unnecessarily long, slog or wasteful of resources due to redundant or poorly optimized code
With the GA4 introduction, many things done in the App GTM Container can now be done in GA4s Add or Modify events or event GTM server-side request modification
Unless there’s a special reason, it’s usually better to skip GTM for apps.
Testing Your Setup
When it comes to testing, GA4 has the Debug View that allows you to see the data flowing into GA4 from both the Web and App. However, different on the Web, testing Apps can be more difficult due to several steps required.
Testing Web Tracking
To test your website tracking, you’ll need:
Access to GTM (to preview and publish changes)
Access to the website (to check if tags are firing)
Access to GA4 (to see if data is coming through)
Extra tools like Analytics Debugger or Omnibug can help you check that everything is working the way it should.
Testing App Tracking
Testing Apps will depend on the type of implementation done. You may need all - or some - of the accesses below:
1. Developer Tools
Android Studio for Android
Xcode for iOS
Testing platforms like Firebase App Distribution or TestFlight
Installation of Android Studio and Xcode for testing app tracking implementations in simulated or real environments. Keep in mind that if you have a Windows computer, testing with Xcode (iOS) can be more complicated than it seems. This approach also includes the requirements for testing platforms in some cases such as Firebase App Distribution, Beta, or Test Flight. All of those fall into the Physical devices option mentioned below.
2. App Files
You’ll need the app file: APK for Android or IPA for iOS
APKs won’t run on iPhones, and IPAs won’t run on Androids, so you’ll need both types of devices or tools
Access to compiled versions of the app (APK for Android, IPA for iOS) to test tracking without relying on production releases. The same goes for the computer you have on hand. APK will only run on Android and IPA on iOS which means, at least, two computers if you don’t want to have hacky solutions.
3. Physical Devices
Testing should cover both iOS and Android devices to verify event tracking consistency across different platforms. This can be an issue if you have multiple team members in different locations who are required to test the App. For this, you may be able to use virtual devices in multiple testing platforms online but none of them - as of the time of this writing - support the level of information required to test GA4 events.
You can also use apps like Charles Proxy, Proxyman, or HTTP Toolkit to see exactly what data your app is sending.
Conclusion
Tracking users on websites and apps is important, but the process is very different. Websites use tools like GTM and data layers to organize and send data. Apps need SDKs and custom code to do the same job.
To get the best results, you need the right setup and tools for each platform. And don’t forget to test! Good tracking helps you make better decisions and understand your customers more clearly—no matter where they are.
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Web vs. App Tracking in GA4: Key Differences, Tools & Best Practices
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