What the data shows for Google Tag Manager
The numbers here come from third-party-web, an open dataset by Patrick Hulce. It is built from HTTP Archive, which tests millions of pages with Google Lighthouse on mobile settings. Lighthouse records how long each script keeps the browser's main thread busy, and ties that time to the web address the script came from. The dataset adds it up for each company and divides by the number of pages that use it.
We used third-party-web version 0.30.0, published in September 2026, with the HTTP Archive crawl from March 1, 2026. For Google Tag Manager it reports:
- Average script execution time: 1,066 ms per page.
- Usage: 15,022,156 pages in the crawl.
What that row covers
This row counts every script served from googletagmanager.com. That includes the Tag Manager container. It also includes gtag.js, the Google tag. Google's own install snippet for Google Ads loads gtag.js from that same domain. So a page with only the Google Ads tag, and no Tag Manager at all, still lands in this row.
Tags that Tag Manager pulls in from other companies, like Hotjar or the Meta Pixel, are counted under those companies, because their code comes from their own servers. See them side by side in third-party scripts and landing page speed.
What script execution time means for a phone visitor
A phone browser does most of its work in one lane, called the main thread. That lane builds the page, runs scripts, and answers taps. Only one job runs there at a time.
Google's Lighthouse docs say that when the main thread is busy, the page can't respond to user input. Google's Interaction to Next Paint (INP), a Core Web Vital, measures how long a tap waits for the screen to react. Google rates INP good at 200 ms or less and poor above 500 ms.
A container stuffed with old tags keeps that lane busy right when a homeowner is trying to tap your number.
How to keep Tag Manager lean
Do not pull Tag Manager off your Google Ads page to save time. It is often how the conversion tag gets there, and it makes changes easier than editing page code. Clean it instead.
1. Keep what you actually use
- Remove dead tags. Old pixels from ended campaigns, a chat tool you dropped, a test tool from two years ago.
- One Google tag. Google Ads Help says not to add more than one Google tag to each page. Check that it is not both hard-coded and in the container.
- Limit tags to pages that need them. A tag that only matters on your blog should not fire on the ad page.
2. Fire extras after the page loads
Tag Manager has page view triggers that fire at different times. Google's Tag Manager Help lists them in order: Consent Initialization, Initialization, Page View, DOM Ready, and Window Loaded. Google says Window Loaded fires after the page has fully loaded, including embedded resources such as images and scripts.
Move nice-to-have tags, like heatmaps and social pixels, to Window Loaded or to a timer. Your headline, phone number, and form get the lane first.
3. Keep the conversion tag early
Do not push your Google Ads conversion tag or conversion linker to the back of the line. Those are what tie a lead to a click. Speed up everything around them, not them.
Check the page after every container change
Containers change quietly. Someone publishes a new version, and the ad page gets a new script nobody reviewed. That is why a check after each publish beats a one-time audit.
ClickMend checks the page your Google Ad sends people to. It gives a 0 to 100 score that blends Google PageSpeed Insights performance (40%), Core Web Vitals (25%), SEO basics (20%), best practices (10%), and accessibility (5%). It names unused JavaScript and other slow parts. It checks tracking too: is the Google Ads conversion tag there, did it load, is the conversion ID a placeholder, is Google Tag Manager missing, is the conversion linker off.
Scan the landing page free, 2 scans a week, no card. Paid plans add weekly monitoring with alerts, covered in landing page monitoring. If conversions look off, read Google Ads conversion tracking not working.
Frequently asked questions
Should I remove Google Tag Manager to speed up my landing page?
Usually no. It is often how the Google Ads conversion tag loads. Clean out unused tags and fire extras later instead.
Does the 1,066 ms include my Google Ads tag?
The dataset counts every script served from googletagmanager.com. Google's own install snippet loads gtag.js from that domain, so the Google tag is part of the row.
Which Tag Manager trigger fires latest?
Google's Tag Manager Help says the Window Loaded trigger fires after the page has fully loaded, including embedded resources such as images and scripts.
Does ClickMend check Tag Manager?
Yes. It flags when Google Tag Manager is missing, checks that the Google Ads conversion tag loaded, and names unused JavaScript. It does not open your container.