How to Test Your Website with Google Lighthouse: The Ultimate Guide

As an expert in web performance and quality, I‘m thrilled to walk you through using Google Lighthouse.

Lighthouse is a gift for geeks like us! This free tool from Google can seriously boost your website across the key metrics we care about – speed, user experience, accessibility, and search optimization.

In this comprehensive guide, I‘ll share everything I‘ve learned from extensive hands-on experience auditing sites with Lighthouse. My goal is to provide tons of insights and data so you can master Lighthouse and create an awesome website.

What Exactly is Lighthouse?

Lighthouse is an open-source automated tool created by Google for improving web page quality. It audits web pages and generates detailed reports on how well pages are performing across a number of categories.

Let‘s quickly walk through what makes Lighthouse so valuable:

Automated auditing – Lighthouse uses automated tooling to catch issues and opportunities that impact site visitors. No more guessing what needs improvement!

Performance metrics – Lighthouse tracks all the vital performance metrics we care about like Time to Interactive and Speed Index. This helps us benchmark and boost page speed.

Actionable suggestions – The best part is the specific suggestions and links to documentation on improving every metric. Now we know exactly what to fix and how.

Scoring – We get an overall 0-100 score plus granular scoring for each category. These quantitative benchmarks help us prioritize improvements and track progress over time.

Custom audits – Run customized audits focused only on the categories you care about, like performance or accessibility.

Shareable – The report formats allow us to share data across teams to align priorities.

Lighthouse can run as Chrome extension, from DevTools, CLI, or even integrated right into our CI/CD pipeline. It works on real production pages, including complex modern web apps.

Overall, Lighthouse gives us the insights needed to methodically enhance our websites. Let‘s look at why we should test with Lighthouse and how to interpret the results.

Why Lighthouse Is Valuable for Your Website

Here are 5 key reasons every site owner should be using Lighthouse:

1. Find performance opportunities

Performance impacts so much – conversion rates, engagement, and even search ranking. Lighthouse reveals exactly how to speed up our page load time and Time to Interactive. We can actually see network requests, JavaScript execution times, and other data to pinpoint optimizations.

2. Improve user experience

Beyond performance, Lighthouse audits for accessibility, SEO, best practices and progressive web app features. Catching these types of issues lets us refine the experience and remove pain points for our diverse users.

3. Prepare for Core Web Vitals

Google will soon make Core Web Vitals like LCP, FID and CLS a ranking factor. Thankfully Lighthouse checks many of these already so we can get ahead.

4. Quantitative benchmarking

The category scores provide a standardized way to benchmark different site versions over time. We can validate that new features or redesigns aren‘t accidentally regressing metrics.

5. Share data across teams

The reports allow us to share performance data across teams from engineering to marketing. Now we can align on priorities using a common language.

Let‘s now walk through exactly how to run Lighthouse and interpret the wealth of data it provides.

Running Lighthouse Audits

The first step is running Lighthouse against your own site to generate reports.

There are a few different ways to run audits depending on use case:

In Chrome DevTools (easiest)

My personal favorite way to run Lighthouse is directly in Chrome DevTools:

1. Open the page to test in Chrome.
2. Launch DevTools (Ctrl+Shift+I on Windows/Linux or Cmd+Opt+I on Mac).
3. Click on the Lighthouse tab.
4. Select the audits you want to run.
5. Hit "Generate report" and view the results!

This is great for quick one-off tests during development.

Lighthouse Chrome Extension

The official Lighthouse Extension also makes auditing sites a breeze:

1. Install from the Chrome Web Store.
2. Click the Lighthouse icon in your toolbar to audit any open tab.
3. Configure audit options.
4. See the report instantly.

No need to keep opening DevTools. This workflow helps test multiple pages quicker.

Lighthouse CLI

For advanced usage, we can run Lighthouse from the command line using Node.js:

# Install Lighthouse CLI 
npm install -g lighthouse  

# Run a report
lighthouse https://example.com 

# Output JSON results
lighthouse https://example.com --output=json --output-path=report.json

The Lighthouse CLI has tons of options for configuring output, performance emulation, and selective audits.

Continuous Integration

My favorite way to run Lighthouse is directly in continuous integration workflows. There are plugins for popular CI/CD systems:

• Jenkins Lighthouse Plugin
• Lighthouse CI for CircleCI
• Lighthouse CI Github Action

Adding Lighthouse to CI enables automatically catching regressions before they impact users. We can even set score thresholds required to pass builds.

Third-Party Tools

There are also handy third-party tools and services that provide Lighthouse testing:

• WebPageTest – Lighthouse testing from geo distributed locations.
• Sitebulb – Web crawler that audits sites using Lighthouse and other tools.
• SpeedCurve – Continuously monitor site performance with Lighthouse.
• Calibre – Schedule Lighthouse tests as part of performance budgets.
• Checkbot – Browser extension to test accessibility using Lighthouse.

These tools provide additional analytics, historical tracking, email notifications, and geographic testing capabilities.

Phew, lots of ways to run Lighthouse! Now let‘s dive into interpreting all the data it returns.

Decoding Your Lighthouse Report

Once your Lighthouse report finishes generating, it‘s time to interpret the results!

Navigating the detailed reports can seem overwhelming initially. Here‘s a quick tour of what it all means:

Overall score

At the very top of the report is your overall numeric score from 0-100:

This single number provides a general sense of how well the page did across all the audits. It‘s calculated as your total earned points divided by the total possible points.

There aren‘t official thresholds, but aim for scores in the 90s when starting out. You may choose to establish internal score targets for your site – for example, requiring overall scores above 85 to pass.

Category scores

Just below the overall score is the breakdown of scores per category:

These provide a high-level view of problem areas. Low category scores warrant further investigation. You may choose to tackle fixes category-by-category based on business priorities.

Lighthouse performance metrics

Within each category are the specific audits and metrics evaluated by Lighthouse:

This is the good stuff! Each audit includes a description explaining why it matters and how it impacts the user experience.

Focus first on audits labeled "Needs Improvement" – these reveal opportunities for quick wins. Even for audits marked as "Passed", we sometimes can still improve the underlying metric.

Diagnostic information

In addition to surfacing issues, Lighthouse provides useful info to help diagnose the root cause:

• The Performance section has traces, network requests, and granular details on costly browser operations.

• The Accessibility section displays impacted nodes in the Accessibility Tree.

• Best Practices call out specifically where each recommendation should be addressed in the code.

• SEO highlights the exact tags, attributes, and pages causing defects.

Digging into these details helps uncover why a particular audit failed and how to address it.

Passed audits

It‘s also important to look at audits that passed. These indicate positive aspects of your site to sustain:

With an everchanging web, scores naturally fluctuate as features are added or new frameworks adopted. Tracking passed audits helps make sure existing capabilities aren‘t accidentally regressing.

Additional metrics

Supplementing the Lighthouse categories are some additional metrics:

• First Contentful Paint – When primary content first rendered.
• Time to Interactive – Time until page is fully interactive.
• Speed Index – Visual completeness of the load.
• Total Blocking Time – Sum of all periods where main thread was blocked.
• Largest Contentful Paint – Render time of largest visible element.

These measurements come from the Navigation Timing API and User Timing API and give additional insight into loading performance.

Phew, that‘s a lot of data! Next let‘s talk about how to actually improve those scores.

Boosting Your Lighthouse Scores

Now for the fun part – taking action on the report to optimize your site!

Here are my top tips for increasing your Lighthouse scores:

Prioritize low category scores

Sort categories by lowest score to prioritize tackling those problem areas first.

Review technologies used

If using frameworks, CMS, CDNs, or 3rd party scripts research if they have Lighthouse-specific optimization guidance.

Start with "Opportunities"

The items labeled "Opportunities" offer easier quick wins vs. more advanced "Diagnostics".

Follow audit recommendations

The "Learn More" link on audits links to official fix documentation from Google.

Retest after changes

Rerun Lighthouse after each improvement to quantify the impact.

Check PageSpeed Insights

Google PageSpeed Insights provides additional tailored Lighthouse optimization suggestions.

Try automated tools

Consider automated tools like Lighthousebot that help fix common issues.

Focus on user experience

Always focus on fixes that meaningfully improve real user experiences, not gaming scores.

Integrate Lighthouse into processes

Add Lighthouse to your development, testing, and deployment processes.

Improving Lighthouse scores takes time and an iterative approach. The key is using the insights to enhance user experience, not hitting arbitrary scores.

Next let‘s cover some tips for getting accurate and consistent Lighthouse results.

Tips for Accurate Lighthouse Audits

To get the most representative Lighthouse results:

Audit production sites

Use live deployed sites, not local or staged environments. This provides realistic results.

Test mobile experience

The mobile audit is more strict; desktop misses responsive issues. Test mobile to catch all UX problems.

Clear browser cache

Cache can alter results, so test in incognito or clear cache before each run.

Disable extensions

Browser extensions that block scripts/CSS interfere with metrics. Disable them while testing.

Close unnecessary tabs

Extra open tabs consume machine resources. Close them for most accurate scores.

Throttle CPU

For mobile tests, enable CPU throttling to simulate mobile processors.

Use repeatable parameters

If possible, use fixed URL parameters instead of unique ones for consistent results.

Understand variability

There will be minor run-to-run variance in scores. Look at the big picture trends.

Compare appropriate sites

Don‘t directly compare scores across vastly different sites – instead, compare similar sites or past versions.

These tips will surface the most valuable opportunities for your particular site and use case.

Now that we know how to run and interpret Lighthouse, let‘s talk about how we can integrate it into our development lifecycle.

Integrating Lighthouse into Your Process

The most effective way to use Lighthouse is baking it right into your software delivery workflow.

Here are some ideas to truly ingrain Lighthouse across your process:

Add to pre-commit hooks

Catch regressions before they even hit the repo by adding to pre-commit hooks.

Include in test suites

Add Lighthouse to integration and regression test suites to gate deployments.

Build a Lighthouse dashboard

Visualize Lighthouse scores over time on a monitoring dashboard for awareness.

Set score thresholds and alerts

Establish score targets and alerts when key metrics fall below the bar.

Review in planning meetings

Include Lighthouse results in performance planning and review meetings.

Load test with Lighthouse

Use Lighthouse during load or integration testing to validate impacts.

Compare with RUM data

Spot insights by comparing Lighthouse metrics with RUM analytics.

Monitor for regressions

Implement alerts when scores decrease compared to baselines.

Ingraining Lighthouse scores into our workflows and processes enables driving sustainable gains over time.

Now that we‘ve covered getting started with Lighthouse, let‘s briefly discuss some key limitations to be aware of.

Lighthouse Limitations

While extremely useful, Lighthouse does have some limitations:

Lab testing only

Lighthouse audits individual pages one-at-a-time in pristine lab conditions with no other traffic. Real user experiences vary.

No real-world factors

It can‘t model real-world network reliability, server load, geographic location, and hardware differences that impact real users.

JavaScript rendering differences

Complex web apps may render differently than Lighthouse based on user interactions and browser extensions.

False positives

Some audits flag issues that don‘t actually negatively impact users. Focus on fixes that meaningfully improve experience.

Not comprehensive

Lighthouse doesn‘t cover every single aspect of performance, quality, and security.

Point in time

Scores reflect performance at the moment tested; ongoing changes can quickly regress.

The best practice is using Lighthouse in combination with other tools like RUM data, synthetic monitoring, and manual testing. View it as an optimization tool, not the single source of truth.

Wrapping Up

Lighthouse provides awesome free auditing of web pages right from within Chrome. The wealth of metrics it provides help systematically improve user experience and quality.

Focus first on the low-hanging fruit – the Lighthouse "opportunities" with the biggest impact. Implement fixes iteratively and integrate Lighthouse into your processes.

Now that you know how to analyze reports and optimize scores, give Lighthouse a try yourself! I hope you found this guide helpful. Let me know if you have any other Lighthouse questions.