The State of
Tag Performance

Simon Hearne

Web Performance Consultant

We pitch ad blockers on speed

Experience a cleaner, faster web

AdBlock Plus

Opera will speed you up on the web and make sure ads don’t distract you from what matters


..control over ads and tracking technologies to speed up page loads


Users want speed

Top Motivations for Using an Ad Blocker:

  1. Too many ads (48%)
  2. Irrelevant ads (47%)
  3. Ads are intrusive (44%)
  4. Viruses / bugs (38%)
  5. Ads take up space (38%)
  6. Improve page load speed (33%)
  7. Avoid video ads (29%)
  8. Privacy concerns (26%)
  9. Preserve data budget (23%)
  10. Preserve device battery (23%)

GlobalWebIndex Q3 2018

Coming Up:

  1. The Importance of Speed
  2. Getting Speed Data
  3. Tags?
  4. Tag Performance
  5. The Impact of Ad Blockers

Data Source 1 πŸ“Š

Akamai mPulse

Data Source 2 πŸ“Š

HTTP Archive

The Importance of Speed

Speed matters

The BBC loses an additional 10% of users for every additional second it takes to load
Pinterest improved load time by 40% and saw 15% increase in SEO traffic and 15% increase in conversions
The Financial times increased user engagement by 30% when they released the new, performance focused FT.com


Speed Correlates with Engagement

~1Bn mPulse pageview beacons - early March 2019

Getting Speed Data ⚑️

Collecting Data πŸ”Ž

Ad Hoc πŸ› 
  • Developer Tools
  • PageSpeed Insights
  • WebPageTest
Synthetics πŸ€–
  • Rigor
  • Catchpoint
  • SpeedCurve
RUM πŸ₯ƒ
  • Analytics?
  • APM
  • mPulse πŸ‘

Data Points

Resource Timing API Level 2 - W3.org

A Willing Victim

Gotchas 1/3

The Timing-Allow-Origin response header specifies origins that are allowed to see values [..] which would otherwise be reported as zero due to cross-origin restrictions.


Gotchas 2/3

all content loaded from cross-origin IFRAMEs (and below) are completely hidden to ResourceTiming.

Cross-origin IFRAME opting-in to sharing ResourceTiming data

Gotchas 3/3

Ad Block detection on one national publisher,
with a narrow demographic.



1/4 of web pages have
>90% third-party requests

HTTP Archive

Tags serve business goals πŸ’΅

  • πŸ’Ή Measurement & Analytics
  • πŸ§ͺ Personalization & Testing
  • πŸ’¬ Comments & Live Chat
  • 🏷 Tag Management
  • πŸ’Έ Ads & Retargeting

"Who put Facebook on the site?!"

Tags can get out of control 😱

  • 352 Requests
  • 147 Domains
  • 2,300kB (1,700kB tags)


Tag managers are enablers

Ad Networks are greedy

So what?


Tag Performance

What's the Risk?


What's the Risk?



Lucky they're always fast, right?

What's the Risk?


The Impact of Ad Blockers

Positive, right?

A simple test


What about the wild?


8.98% pageviews with ads blocked (n=50M)

MetricWith AdsWithout AdsDifference
Page Load Time (ms)6,1304,600-25%
Time to Interactive (ms)5,4804,260-22%
LongTasks Time (ms)1,270241-81%
First Input Delay (ms)868-93%
Page Size (MB)2.691.99-26%
Bounce Rate68.8%67.0%-2%
Time on Site (s)410708+72%
Session Length (pages)2.804.41+58%
JavaScript Errors per Page1.920.18-91%


  • Third-party tags are pernicious
  • Ad Blockers significantly improve performance
  • Users with Ad Blocking enabled engage more

Thank you πŸ™

  • πŸ“§  simon@hearne.me
  • πŸ“£  @SimonHearne
  • 🌎  simonhearne.com