Google Analytics 4

[GTM] Data Layer Common Problems and Viable Solutions

Mark Anthony Tamayao
December 21, 2023


The Data Layer is a technical term that may be hard to understand, but it's simply a collection of data about your website and its visitors that Google Tag Manager (GTM) uses to track and manage. Let's explain it in a way that's even easier to understand. Imagine the Data Layer as a train station. Different types of data (like page views, product views, and purchase events) are like trains that arrive at the station. GTM is like the train controller, directing the trains to the right platforms.

In other words, the Data Layer is a central repository for all of your website's data that can be retrieved and used by different tracking tools, such as Google Analytics. Instead of relying solely on HTML elements or JavaScript events to capture data, the Data Layer provides a structured and organized way to collect information, making it easier to track user actions accurately.

The Data Layer is a powerful tool for tracking, but it's only effective if you understand and implement it correctly. That’s why we created this blog post; here, we are going to explore the Data Layer in detail, discuss common problems and mistakes, and share best practices for a seamless implementation.

Table of Contents  

  • Implementing the Data layer in GTM

                 - Data Layer Variables

  • Common issues/Mistakes and How to Fix Them
  • Best Practices
  • Tools to Debug and Verify DataLayer Push
  • Frequently Asked Questions
  • What are the next steps?
  • Final Word

Implementing the Data layer in GTM

To set up the Data Layer, ask your developer to add this code snippet to the <head> section of your website above your container snippet.

    window.dataLayer = window.dataLayer || [];

Once you've placed the Data Layer snippet on the right section of your website, we can move on to the next step. But first, let's explain how the Data Layer actually works. Every trigger in Google Tag Manager (GTM) uses the Data Layer. For example, on this blog homepage for Analytics Mates, we could use the Data Layer to track events such as page views, button clicks, and form submissions.

GTM can then use the Data Layer to fire tags when certain events occur. For example, we could create a trigger that fires a Google Analytics tag whenever a user clicks on a link to a different page on our website.

Here’s a visual representation of it: 

The next step is to push data (information) into the data layer. Here is a simple example of how to push the author of a blog post once a visitor clicks on that particular blog post link using the dataLayer.push() method:


window.dataLayer = window.dataLayer || [];


'event': 'Blog View',

'Author': 'Gary Spagnoli',

'Blog Post Title: 'How to Set Up Standard and Custom Reports in GA4'



Data Layer Variables

Google Tag Manager does not automatically recognize custom data in the data layer. You cannot use regular variables to store custom data from the data layer. To use custom data, you must create a data layer variable. Here are the steps:

Once you have the key that you would like to work with, you can proceed to create a data layer variable:

  1. Click Variables.
  2. Under User-Defined Variables, click New.
  3. Click Variable Configuration and select Data Layer Variable as the variable type.
  4. In the Data Layer Variable Name field, enter the key exactly as it was written in the code (e.g. Author, not Blog Author.)
  5. In most cases you should leave the Data Layer Version set to the default value of Version 2. Learn more.
  6. Save the variable.
  7. Repeat these steps for every data layer key that you would like to have available as a variable in Tag Manager.
  8. Publish the container.

 Note: Data Layer Variable Name field is case sensitive, this is because that is the name of the parameter that is stored in the data layer.

Now that we’re all set, the next step would be to check if the variable will come up in the preview and debug mode in GTM.

And yep, it’s there!

Once the data has been pushed to the data layer, you can retrieve it and use it to generate reports, such as a Google Analytics report that tells you which author's content has the most engagement.

To use this parameter, you can either create a new GA4 event tag or add it to an existing one. In this example, I’m adding to our existing event tag, “Blog Views”.

You can check it once again using Preview and debug mode in GTM. 

Make sure, to that you’ll take an action that will trigger the tag. In this scenario, just clicking any blog post. And you should be able to see the new variable in the preview mode - like this:

You can also confirm that the data has been passed to GA4 by checking the DebugView section.

That's it! You can reuse the same steps to add more data parameters via the data layer and pass them to GA4, which can be used to generate more custom reports.

Common issues/Mistakes and How to Fix Them

Missing and Incorrect Data

The most common problems with the Data Layer are either mismatched data or missing data. This can be very frustrating, but it can be prevented and fixed if you follow all the best practices and implement the Data Layer correctly. Sometimes, you've checked everything and you're sure that there's nothing wrong with the setup, but the problem persists. So, we've collected some of the known Data Layer issues that you may be facing.

1) When it comes to Ecommerce tracking, it must be formatted correctly based on this documentation. Here are some few points you need to pay attention:

  • Make sure that all values are formatted correctly. For example, if a value is a string (i.e., text), it should be surrounded by quotation marks. 
  • Example:
  • Follow the steps and make sure that all required fields are used. You can check the Google Analytics and GTM documentation to see which parameters are required and which are optional.
  • As shown in the example above, be mindful of currency signs (e.g., $9.99) when entering prices. No need to use it.
  • A single symbol or character can cause problems. For example, item_id: ‘SKU_12345’ is different from item_id: “SKU_12345”.

2) Another common mistake is missing transactions due to redirection during check out steps.

If you are using Google Tag Manager (GTM) and Google Analytics 4 (GA4) to track transactions, you need to push purchase information to the Data Layer when the purchase is complete. If the user is redirected to a "Thank you" page, that is where you should activate the dataLayer.push() command.

To ensure that purchase data is being passed to the Data Layer when a purchase is made, verify that the format and values are correct. If you have hardcoded tracking implemented in your website, check that this code is sending purchase data into the Data Layer. You can use tools like those mentioned in this blog post to verify this.

3) Sometimes, data layer variables are not populated when the page loads, or data layer events do not trigger the correct tags in Google Tag Manager.

In other words, the data that is stored in the Data Layer is not always available to Google Tag Manager when it needs to be. This can happen for a number of reasons, such as:

  • The data layer variables have not been declared correctly.
  • The data layer variables are being populated after the page has loaded.
  • The data layer events are not being fired correctly.
  • The data layer triggers in Google Tag Manager are not configured correctly.

If you are experiencing this issue, you can troubleshoot it by using the following steps:

  1. Check that the data layer variables have been declared correctly. You can do this by using the Google Tag Manager Preview and Debug mode.
  2. Check that the data layer variables are being populated before the page has loaded. You can do this by using the Google Tag Manager Preview and Debug mode to set a breakpoint on the data layer variable and then inspect the variable value.
  3. Check that the data layer events are being fired correctly. You can do this by using the Google Tag Manager Preview and Debug mode to set a breakpoint on the data layer event and then inspect the event data.
  4. Check that the data layer triggers in Google Tag Manager are configured correctly. You can do this by reviewing the trigger configuration settings.

4) Placement could make a big difference.

Move the Data Layer snippet above the container snippet to ensure that variables pushed to the Data Layer can fire tags on page loads with a matching condition.

Therefore, it is important to place the Data Layer snippet above the container snippet so that tags can access the data they need to fire correctly. It should look like this:

Duplicate Data

One of the most common mistakes is data duplication, which can be caused by incorrect implementation. You can easily catch these errors by leveraging the GA4 Real-time Reporting, Event Debugging tools and Chrome Dev Tools (check more of this below).

When the same event is pushed to the Data Layer multiple times, it can cause duplicate Data Layer events, which can lead to duplicate events being sent to Google Analytics 4 (GA4). Imagine you're seeing duplicate "add_to_cart" events in your GA4 Debug View. This means that the events are being sent when a user clicks the "Add To Cart" button and a "DataLayer.push" is triggered. This makes the click information visible in preview mode.

To fix this, make sure that events are not being pushed to the Data Layer multiple times on the same page. You can do this by examining your website's code to find any instances where the same event is being pushed more than once.

Privacy Issues

Privacy concerns related to the Data Layer and Google Tag Manager (GTM) primarily focus on data collection, user consent, and compliance with privacy regulations such as the General Data Protection Regulation (GDPR) and the California Consumer Privacy Act (CCPA). However, GTM assures users that it is compliant with these regulations and will continue to ensure that its practices are in accordance with the latest requirements.

We just need to be careful in making sure that we’re not adding sensitive information to the data layer such as credit card information, names and email address/es – These are all considered Personally Identifiable Information (PII). Information such as credit card numbers or passwords. Remember that anyone who views your website's source code can see this information. 

Forgetting about case sensitive data

The dataLayer object name is case-sensitive: If you try to push a variable or event without the proper casing, the push will not work.

Here’s an example: 

datalayer.push({'pageTitle': 'Home'});    // Bad (datalayer in lowercase)
dataLayer.push({'pageTitle': 'Home'});    // Good (dataLayer in camel case)

Tools to Debug and Verify Data Layer Push

Developer tools: Most web browsers have built-in developer tools that can be used to inspect the data layer. For example, in Chrome Dev Tools:

  1. You can open the developer tools by pressing Ctrl+Shift+I on Windows or Cmd+Opt+I on Mac. 
  2. Then, click the Console tab and 
  3. Type dataLayer to view the data layer object.

Browser extensions: There are a number of browser extensions that can help you debug the data layer. Some popular options include:

  • Tag Assistant: This extension from Google can help you identify and troubleshoot problems with your Google Tag Manager tags and triggers.
  • Data Layer Checker: This extension allows you to inspect the data layer without having to open the developer tools.
  • Data Layer Inspector: This extension provides a detailed view of the data layer, including all of the data layer variables and their values.

Tag management systems: Tag management systems (TMS) such as Google Tag Manager (GTM) provide built-in debugging tools for the data layer. For example, in GTM, you can use the Preview and Debug mode to see how the data layer is being populated as you interact with a page.

Best Practices

Aligned Goals with the Web Developer while Working Closely with Them

Aligning goals with web development teams is a crucial best practice when working with the Data Layer in Google Tag Manager (GTM). Collaboration and effective communication between marketing or analytics teams and web developers can significantly enhance the success of your GTM implementation. 

How to align goals with web developers:

  • Communication: Start by establishing open and regular communication channels with the web development team. Clearly convey your tracking requirements and objectives.
  • Collaboration: Involve web developers in the planning phase of your GTM implementation. Discuss the Data Layer structure and events before implementation begins.
  • Documentation: Create clear and comprehensive documentation that outlines the Data Layer structure, variable naming conventions, and expected events. Share this documentation with the web development team.
  • Testing: Collaboratively test the Data Layer implementation to ensure that data is being captured accurately and that it meets your tracking requirements.
  • Feedback: Maintain an ongoing feedback loop with web developers. If there are changes to the website that impact the Data Layer, communicate these changes promptly to ensure that tracking remains accurate.

Using Proper Debugging Tools

Debugging helps you ensure that your Data Layer implementation is working as expected and that you are collecting the correct data. It can also help you quickly identify and resolve any issues that may arise.

And why is this approach important?:

  • Error Identification: Debugging tools help you identify and pinpoint errors or issues in your Data Layer implementation. This includes problems with variable values, event triggers, or conflicts.
  • Validation: Debugging allows you to validate that the data you're sending to GTM via the Data Layer is accurate and matches your tracking requirements.
  • Efficiency: Debugging tools streamline the troubleshooting process. Instead of relying solely on manual inspection, you can use these tools to quickly identify and diagnose problems.
  • Real-time Testing: Debugging tools often provide real-time feedback, which means you can see how data is flowing through the Data Layer and GTM in real-time as users interact with 

Regular Audits of Data 

Audits help you maintain the quality and accuracy of the data collected through your GTM implementation. 

Here's why regular audits are crucial and how to conduct them effectively:

  • Data Accuracy: Audits ensure that the data being collected via GTM accurately reflects user interactions and website behavior. This is essential for making informed business decisions.
  • Data Quality: Regular audits help maintain data quality by identifying and rectifying any discrepancies, missing data, or inconsistencies in your tracking setup.
  • Compliance: Data audits can help ensure that your data collection practices are compliant with privacy regulations such as GDPR or CCPA. This is especially important for avoiding potential legal issues.
  • Tag Management: Over time, websites may change, and new features may be added. Regular audits help you confirm that your GTM container and Data Layer remain aligned with the current state of your website.

Frequently asked questions

Should dataLayer come before or after GTM?

Answer:  It’s very important that the Data Layer snippet is placed above Google Tag Manager’s container code in your website’s code. If the snippet is placed after the GTM container code, the data won’t be fetched by Google Tag Manager.

Can I push data into the Data Layer dynamically?

Answer: Yes, you can push data into the data layer dynamically using JavaScript. This lets you update the data layer with real-time information based on user interactions and other website events.

Why is the Data Layer important in GTM?

Answer: The Data Layer is essential in GTM because it enables you to access and utilize structured data from your website, making it easier to implement tracking codes and customize tags without having to modify the website's code directly.

What are the next steps: 

If you've reached this section of the page, congratulations! You're awesome. There may still be some areas you're not confident in, but you're on the right track. We believe you can gain more knowledge, and here are some resources to help you continue learning:

Final word: 

So, we've explored the Data Layer and its role in tracking and managing data on your website. We've also discussed common challenges and pitfalls, and shared best practices for a seamless implementation. Remember Data Layer is a central repository for your website's data, making it easy for tracking tools like Google Analytics to access and use this information. It should eliminate the need to rely on scattered HTML elements or JavaScript events, providing a structured and efficient way to capture data accurately.

With what you've learned in this post, you can now use the Data Layer to track and analyze data on your website more effectively. We encourage you to apply these insights to your website today. We hope that this will help you improve the accuracy of your data tracking, make better decisions, and have a stronger online presence.

If you have any further questions or need additional guidance, please don't hesitate to reach out. We're here to help you navigate the intricacies of the Data Layer and take your digital endeavors to new heights.

Thank you for reading!

We're always looking for ways to improve our Google Analytics 4 blog content. Please share your feedback so we can make it even better.

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Mark is a Xoogler, and former web developer who discovered his true passion for Analytics along his professional journey. With a natural inclination for problem-solving, he dedicated five years to refining his web development skills before immersing myself in the world of Google Analytics in 2010. Throughout his career, he’s had the privilege of working with renowned companies that have greatly contributed to his growth in the field of Analytics.

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