A dataLayer Guide Marketers Need: What It Is, How It Works, and When to Implement It

What is dataLayer and when should you use a dataLayer?

A dataLayer is simply a layer of data — a structured place where your website can store and pass the information you actually want to track.

Before diving deeper, let’s revisit how a webpage works. When a page loads, all its information appears in the HTML as static text (you can see this by using “view page source”). But tracking tools don’t need everything in the source. They only need a few key pieces: URL, title, category, CTA labels, and so on.

Instead of sifting through the entire page source, a separate “information layer” can hold just the useful data. This is the dataLayer, maintained by your dev team.

Google describes the dataLayer “as a structured way to pass information from your site to your tags so events and variables can be used to trigger tracking”.

Simo Ahava explains it “as a dedicated structure that holds the data you want to pass from your website to your analytics and marketing tools — keeping that information separate so changes on the page don’t break your tracking.”

The dataLayer doesn’t appear visually on the page because it’s not meant for users. It exists in the code and can be seen in developer tools, but not in the UI.

How does it look like?

A dataLayer entry looks like a simple JavaScript object — key–value pairs wrapped in curly brackets. For example:

{
name: "PK",
age: 30
}

Here, name and age are keys, while "PK" and 30 are values.
A dataLayer follows the same structure but usually contains more information. Example:

{
       event: "gtm.load",
       gtm: {
            uniqueEventId: 56,
            start: 1764248590730
            }
}

Values can be any valid JavaScript type, including objects.

To view the dataLayer:

1. Right-click → Inspect
2. Go to Console
3. Type: dataLayer
4. Press Enter

If the page has a dataLayer, you’ll see it.

Difference between non-dataLayer tracking and dataLayer tracking

Using a dataLayer when it’s not required mainly costs time. Your tracking still works either way, but a clean dataLayer often produces more reliable and consistent results.

Non-dataLayer tracking = reading values directly from the page (elements, attributes, button text, click events, URLs).

dataLayer tracking = collecting those values plus information triggered by user actions that isn’t visible in the HTML — for example, when someone plays a video.

As Simo points out, relying on information scattered across the page creates a risk: if the website changes, your tracking breaks. A dedicated dataLayer keeps that data separate and stable.

Do you need dataLayer?

Tracking typically involves three steps:

1. Identifying the events you want to measure
2. Extracting the “information of interest” for each event
3. Sending that information to your destination in the correct format

Sometimes the information is readily available in the browser (e.g., CTA text). Sometimes it’s not — like a discount code used during checkout.

This is exactly when a dataLayer becomes useful.

Ideally, you finalize your measurement plan before deciding whether you need a dataLayer. In some cases, you may know this earlier for example, when the site has dynamic interactions.

A helpful rule: if you want to send the same events to multiple platforms, a dataLayer gives you one central source of truth and keeps values consistent across systems.

Real-world scenarios where this applies

1. Ecommerce transactions (common case where dataLayer is needed)

In ecommerce, a dataLayer is often essential because many order details — such as transaction ID, order value, items purchased, categories, and upsell activity — are not present in the page source. After the transaction is processed, developers push these values into the dataLayer so tracking tools can read them in a structured way.

2. Dynamic forms (may need a dataLayer)

If you’re using a HubSpot form with dynamic behaviour — for example, a date selection that reveals new fields — a dataLayer can help pass those internal selections to your tracking tools.
But for simple, static HubSpot forms, non-dataLayer tracking is usually enough.

3. Cross-platform tracking (dataLayer improves consistency)

When sending events to multiple platforms like Google Ads, Facebook, or LinkedIn, a dataLayer helps ensure the event names and values stay consistent.

It’s technically possible without a dataLayer, but far more fragile and time-consuming.

Why this decisioning is important

dataLayer work typically depends on your development team. If most of your measurement involves basic interactions like form submissions or button clicks  and you’re not sending data to many platforms – marketing teams can often implement tracking themselves for a much faster turnaround.

When you do, do you just use the dataLayer?

You don’t have to. Tracking can also be a hybrid of both dataLayer and non-dataLayer set ups.

For example, if your marketing team wants to test a simple on-page variation like a video hero vs a screenshot of your SaaS product*, you may want to send the results to Google Analytics. Developers could modify the dataLayer for this, but temporary changes consume time and need to be reversed later. In such cases, it’s usually faster for marketing to track this directly without the dataLayer.

*Acc to an analysis by DoWhatWorks, video lost to image and product videos are a weak bet 😉

While a dataLayer is extremely useful for long-term, scalable tracking, match the approach to your resources, timelines, and whether the change is temporary.

Why is it written as “dataLayer” (lowercase d, uppercase L)?

dataLayer was popularized by Google Tag Manager.
Although you can name your data layer anything — and even have multiple layers on one page — each one needs a unique name. GTM standardized dataLayer, and it became the common convention.

Decision Checklist (use this before implementing a dataLayer)

Use a dataLayer if:

• The value you need is not visible in the page source
• The data appears only after a user interaction
• Multiple platforms need the same event
• The event is long-term and part of your main measurement plan
• Your site design changes frequently which means classes, IDs and HTML elements might change
• You need structured data like in ecommerce set ups (purchase ID, items, totals) tracked

You can skip the dataLayer if:

• The values you need are already visible on the page
• The event is short-term (e.g., you’re testing something or a temp landing page)
• Marketing can track it directly in GTM
• The element is static and only requires basic click tracking
• You’re collecting simple UI interactions like scrolls, link clicks, form submissions