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Monitoring website quality with Lighthouse

Watchful integrates Google Lighthouse to help you measure and monitor the quality of your websites. Lighthouse analyzes important aspects of website performance, accessibility, search engine optimization (SEO), and technical best practices.

Watchful automatically runs weekly Lighthouse scans, records historical scores, and can notify you when website quality declines. You can also launch manual scans to generate detailed reports and investigate problems.

Privacy and data protection

All Lighthouse audits are performed on Watchful’s GDPR-compliant servers, ensuring that your website’s audit data remains within our infrastructure. No audit data is sent to Google, and Watchful does not use any Google APIs to perform these audits.

This allows you to benefit from Lighthouse’s website quality analysis without sharing your audit results or website information with Google.

What does Lighthouse measure?

Lighthouse evaluates your website across four main categories:

  • Performance: Measures how quickly your website loads, becomes visible, and responds to user interactions.
  • Accessibility: Identifies potential barriers that could make your website difficult to use for people with disabilities.
  • Best Practices: Checks for common technical issues involving browser compatibility, security, and modern web development standards.
  • SEO: Evaluates technical factors that affect how search engines discover and understand your website.

Watchful also displays additional Lighthouse assessments, including Agentic Browsing checks, when available.

Each main category receives a score from 0 to 100. Scores are color-coded to make results easier to interpret:

  • Green (90–100): Good
  • Orange (50–89): Needs improvement
  • Red (0–49): Poor

Lighthouse produces separate results for mobile and desktop devices, allowing you to evaluate the experience for different visitors.

Running a manual Lighthouse scan

Manual Lighthouse scans generate complete reports, including individual audits, performance metrics, and recommendations for improving website quality.

To run a manual scan:

  1. Open the Sites Dashboard in Watchful.
  2. Locate the website you want to analyze.
  3. Expand the site’s site drawer.
  4. Click Lighthouse Scan to open the Lighthouse report.
  5. Click Scan again in the upper-right corner to launch a new scan.

Watchful starts the scan and displays a progress notification.

A Lighthouse scan typically takes a few minutes to complete. You can continue using Watchful while the scan runs.

Once the scan finishes, the complete report is available for review.

Automated weekly Lighthouse scans

Watchful automatically runs a Lighthouse scan for your websites every week. These scheduled scans help you monitor website quality over time without having to manually initiate each scan.

Automated scans collect and store Lighthouse scores for the four main categories:

  • Performance
  • Accessibility
  • Best Practices
  • SEO

Scores are recorded separately for mobile and desktop devices.

Automated scans are designed for ongoing monitoring and historical comparisons. To minimize the resources required for regular monitoring, Watchful records only the scores from these scans, not the complete Lighthouse reports.

Automated scan results appear in the Lighthouse scan history alongside manual scans.

If an automated scan reveals a significant decline in website quality, you can launch a manual scan to generate a detailed report and investigate the cause.

Enabling Lighthouse performance drop notifications

Watchful can notify you when a Lighthouse scan detects a significant decrease in your website’s Performance score.

To enable these notifications:

  1. Open Settings in Watchful.
  2. Select the Notifications tab.
  3. Find the Connectivity, Uptime & Performance section.
  4. Enable the Lighthouse performance drop checkbox.
  5. Make sure Disable all notifications is set to No.
  6. Click Save notifications settings.

How performance drop notifications work

Watchful uses a threshold of 25% to identify significant performance declines.

The latest Lighthouse Performance score is compared with the site’s average Performance score. A notification is triggered when the latest score is at least 25% lower than the average.

Mobile and desktop scores are evaluated independently. A significant decline on either device can trigger a notification, even if the other device continues to perform well.

For example:

  • If your site’s average mobile Performance score is 80, a new score of 60 or lower meets the notification threshold.
  • If your site’s average desktop Performance score is 96, a new score of 72 or lower meets the notification threshold.

The threshold represents a relative percentage decrease, not a fixed reduction of 25 points. This means the score required to trigger a notification depends on the site’s historical average.

Investigating a performance drop

When you receive a Lighthouse performance drop notification:

  1. Open the affected site’s Lighthouse scan history.
  2. Review the mobile and desktop scores to identify which device experienced the decline.
  3. Compare the latest score with previous results to understand the trend.
  4. Run a manual Lighthouse scan using Scan again.
  5. Review the detailed Performance report to identify potential causes.
  6. Address the issues identified by Lighthouse and run another manual scan to measure improvements.

Automated weekly Lighthouse scans record scores only. They do not retain the complete Lighthouse report.

To investigate a performance decline detected by an automated scan, you must run a manual scan to generate the detailed audits, metrics, and recommendations needed for troubleshooting.

Understanding your Lighthouse report

The Lighthouse report begins with a summary of the website’s scores for both mobile and desktop devices.

The summary table includes scores for SEO, Performance, Accessibility, and Best Practices, making it easy to identify categories that need attention.

Below the summary are two expandable sections:

  • Mobile report
  • Desktop report

Click either section to expand the corresponding results.

Reviewing detailed audit results

Each report includes individual Lighthouse audits that explain how your website performed.

Select a category to review its findings. Depending on the category, Lighthouse provides:

  • Overall category scores.
  • Individual checks that passed or failed.
  • Explanations of identified problems.
  • Recommendations for improving your website.
  • Supporting technical information and links to additional guidance.

Click an individual audit to expand its details.

Lighthouse also groups results into sections such as Passed audits, Not applicable, and Additional items to manually check.

Passed audits highlight checks your website already satisfies. Manual checks identify areas that require human evaluation rather than automated testing.

Understanding performance metrics

The Performance report includes several measurements that help explain the visitor experience.

  • First Contentful Paint (FCP): How long it takes before the first visible content appears.
  • Largest Contentful Paint (LCP): How long it takes for the largest visible content element to render.
  • Total Blocking Time (TBT): How much time the browser’s main thread is blocked by long-running tasks.
  • Cumulative Layout Shift (CLS): How much visible content unexpectedly moves while the page loads.
  • Speed Index: How quickly the visible portions of the page appear.

The report also includes a visual filmstrip showing how the page renders during loading.

Use these measurements alongside the recommendations in the Insights and Diagnostics sections to identify opportunities for improvement.

For example, Lighthouse may recommend optimizing image delivery, reducing unused CSS, or improving cache lifetimes.

Viewing Lighthouse scan history

Watchful maintains a history of both automated weekly scans and manually initiated scans.

This allows you to track website quality over time, identify performance regressions, and measure the impact of website changes.

To view the history:

  1. Open the Sites Dashboard.
  2. Locate the website you want to review.
  3. Expand its site drawer.
  4. Open the Lighthouse scan history using the history control beside Lighthouse Scan.

The history view displays a chart of previous Lighthouse scores, followed by a table listing individual scans.

Understanding the history table

Each row represents a Lighthouse scan, identified by its date and time.

The table displays scores for:

  • SEO
  • Performance
  • Accessibility
  • Best Practices

Each category has separate mobile and desktop scores, indicated by device icons in the column headings.

All scores use the same color-coded scale as the individual Lighthouse reports, making it easy to spot improvements or declines.

The history includes both scan types:

  • Automated weekly scans: Display the recorded scores without a link to a full Lighthouse report.
  • Manual scans: Display the recorded scores and include a link to the full Lighthouse report with detailed findings.

Only manual scans have a complete report available for review.

Use the pagination controls at the bottom of the history table to review older scans.

Analyzing website quality over time

The Lighthouse history chart provides a visual overview of how your website’s scores have changed across successive scans.

Different colored lines represent the four main audit categories.

Use the chart and history table together to identify trends and investigate significant changes.

Identify performance regressions

A sudden reduction in a Lighthouse score can indicate that a recent website change has affected quality.

For example, a drop in the Performance score might be associated with:

  • Installing or updating a plugin or extension.
  • Adding large images or other media.
  • Introducing additional JavaScript or CSS.
  • Changing a theme or template.
  • Modifying caching or server settings.

Compare the scan dates with recent website updates to help identify possible causes.

Compare mobile and desktop performance

Mobile and desktop scores can differ substantially.

A website may perform well on desktop while delivering a slower experience on mobile devices.

Use the separate mobile and desktop columns to determine whether a problem affects both environments or is more pronounced on one.

Measure improvements

After making changes to improve website quality, run another manual Lighthouse scan.

Compare the new results with earlier scans to determine whether the changes improved the relevant scores.

For example, after optimizing large images, you might see improvements in Largest Contentful Paint and the overall Performance score.

Prioritize recurring issues

Not every Lighthouse finding requires immediate action.

Focus on issues that:

  • Consistently receive poor scores.
  • Affect important user interactions.
  • Appear in both mobile and desktop results.
  • Have worsened across several scans.
  • Offer meaningful opportunities to improve loading speed or accessibility.

When you identify a recurring problem, run a manual Lighthouse scan to access the detailed audits and suggested improvements.

Investigating a drop in Lighthouse scores

If Watchful detects a decline during an automated weekly scan, the history will show the lower score, but the full technical report will not be available.

To investigate:

  1. Open the affected site’s Lighthouse scan history.
  2. Review the historical scores to identify the category and device type affected.
  3. Check whether the decline occurred gradually or between two consecutive scans.
  4. Return to the site’s Lighthouse Scan page.
  5. Click Scan again to launch a manual scan.
  6. Open the completed report and review the relevant audits.
  7. Follow the Lighthouse recommendations to address any identified problems.
  8. Run another manual scan after making changes to measure the improvement.

For example, if an automated scan shows that mobile Performance dropped from 92 to 65, run a manual scan and examine the detailed Performance report.

Look for changes in metrics such as Largest Contentful Paint, Total Blocking Time, and Cumulative Layout Shift.

The report may reveal issues such as oversized images, render-blocking resources, or excessive JavaScript execution.

Once the issue is addressed, another manual scan helps confirm whether performance has improved.

Managing scan history

The Lighthouse history table includes a delete control for individual scan records.

Use this control to remove historical results that you no longer need.

Deleting old results may be useful when cleaning up test scans or removing records that are no longer relevant.

Best practices for Lighthouse monitoring

For effective website quality monitoring:

  1. Enable Lighthouse performance drop notifications to receive alerts when performance declines.
  2. Use the automated weekly scans to monitor website quality over time.
  3. Review historical scores regularly to identify gradual changes and recurring issues.
  4. Run a manual scan whenever you need a detailed technical report.
  5. Compare mobile and desktop results to identify device-specific problems.
  6. Run manual scans before and after major website changes to measure their impact.
  7. Focus on significant problems before minor optimizations.

Lighthouse scores can vary between scans because of factors such as network conditions, server response times, and page content. Small differences do not necessarily indicate a meaningful change.

Lighthouse is also an automated auditing tool. Its accessibility and technical assessments are useful indicators, but they do not replace comprehensive manual testing.

Summary

Watchful combines automated weekly Lighthouse scans, performance drop notifications, and detailed manual reports to help you monitor website quality.

Weekly scans provide ongoing score tracking, while Lighthouse history makes it easy to identify trends and potential problems.

When a score declines, a manual Lighthouse scan provides the detailed audits and recommendations needed to investigate and improve your website.

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