Performance Debugging

With DevTools

You can also watch this talk online


This talk:

  • Uses  Canary
  • 🆕 Enables experimental features
  • 👀 Has lots of live demos!

What will we cover?

  1. 🌍 Network Performance
  2. 📺 Render Performance
  3. 👩🏻‍💻Programmatic Performance

Network Performance

Fonts + Local Overrides

Hello online viewer! The part of the talk was a live demo on local overrides. This video explains all

What did we just see?

  • 🖼 Screenshots in the network panel
  • Local overrides + Pretty printing
  • 📖 Font display

Render Performance

Performance 🚀

Was traditionally all in the network


Heavy frontend?

Then say hello to

👋 Render Performance 👋

  • Scrolling smoothness
  • Animation FPS
  • Size of the DOM
  • CSS Complexity
  • Time to interactive
  • Speed of visual progress
  • User input response Times
  • JavaScript parse time
  • JavaScript execution time
  • JavaScript heap size

Fortunately, we have


  • FPS Meter
  • Paint Profiler
  • Paint Flashing
  • Timeline Recorder
  • JavaScript Source Code Profiling
  • Network Timing Breakdown
  • Console Timing
  • Filmstrip Recording
  • Scroll Bottlenecks
  • JavaScript Heap Snapshots
  • JavaScript Allocations
  • CPU Profiler
  • Timeline History
  • Paint Indicators
  • Memory Profiler
  • Layers Panel
  • Performance monitor

These tools can turn something

qualitative  👌

Into something

quantitative  🔢

🐢🐢   "It feels sluggish"   🐢🐢

DevTools can help you


the performance of your webpage

Page Smoothness

With the FPS Meter

JavaScript Execution Cost

Line Level Profiling with three.js

Hello online viewer! This was a live demo of line-level profiling

Breaking Rules

Console Violations

DevTools Audits

Find out:

  • Why the audit is important?
  • How to pass the audit
  • How the audit is implemented

Shareable Audits

With WebPageTest + Lighthouse

A two Minute Performance Workflow

Hello online viewer! This live demo showcased a few bits and pieces. See it at the 17m 35s mark.

Or see lesson 7 of Modern DevTools

Request Blocking is a thing!

Workflow Recap:

  1. 📽   Record perf profile #1

  2. 🚫   Block a script (product) in the Network Panel

  3. 📽   Record perf profile #2

  4. 📊   Compare recording #1 with #2

Find Third Party Scripts

Product Badges

Performance Monitor

Hello online viewer! This part of the demo showed the performance monitor

Performance Monitor - Why?

  • Quicker + simpler introduction to render performance
  • Capture metrics throughout your complete website usage
  • Drill down into only what you care about - remove the noise

Programmatic Performance

Paint Indicators

Hello online viewer! The part of the demo showed off paint indicators @ 25m 16s.


Want to learn more?

Identify Unused CSS & JS

Hello online viewer! This part of the talk showed off code coverage

Code Coverage Features
  • 👁   Visualise your unused CSS & JS
  • ♻   Real-time updates


Code Coverage

Hello online viewer! This part of the talk showed off using puppeteer to extract code coverage information. You can view and run the code here on GitHub

Monitoring your unused CSS over time?


Thank you