Troubleshoot Missing Metrics or Audits

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What are the common reasons for missing audits and metrics?

Audits or metrics are missing when Lighthouse was not able to collect them during testing due to errors (some of specific errors are documented on the Troubleshooting failing tests page). Commonly, these errors occur when a page has a specific set of characteristics, such as:

• 10,000+ DOM nodes
• Excessive main thread activity
• Activity that causes Chrome browser to become unstable

Why is the Lighthouse Performance Score missing?

The Lighthouse Performance Score is calculated using five metrics:

• First Contentful Paint
• Largest Contentful Paint
• Speed Index
• Cumulative Layout Shift
• Total Blocking Time

If any of these metrics can’t be retrieved by Lighthouse, the Performance Score won’t be calculated. It’s not uncommon for the interactivity (JavaScript execution-related) metrics contributing to the score, such as Total Blocking Time, to not be present in a given test, especially if it’s conducted with mobile Test Profiles. Mobile devices have less capable CPUs, less powerful batteries and different network connections.

For the interactivity metrics to be collected, the JavaScript main thread has to have no activity for a certain period of time (the main thread is at rest). For Time to Interactive, that period is 5 seconds. Missing TTI reading will result in no Total Blocking Time reading, and consequently, no Performance Score.

To make sure Performance Score is collected, we’d recommend having a look at JavaScript performance. You can investigate it on the Long Task Timeline to check for blocking tasks and scripts that might be at fault. You can also profile performance directly in your browser developer tools.

What does Calibre do to ensure maximum information is collected during a test?

Calibre has three test modes that ensure each Snapshot returns key performance metrics, even in cases when Lighthouse raises an error. By default, all tests are run in Standard Mode, however if a test fails due to a Lighthouse Timeout Error, Calibre will automatically re-run the test in Compatibility Mode. Here’s a summary of each test mode type:

• Standard Mode: The default mode for all Calibre tests. All audits, metrics and artifacts are recorded.
• Compatibility Mode: Omits known problematic Lighthouse audits in an attempt to ensure the test completes successfully and performance metrics are recorded. There are two types of Compatibility Modes:
  • Reduced Audits: Omits all non-performance related information. The test will return all paint based, runtime, byte size and request metrics, but will not return Accessibility, SEO or Best Practices scores and audits.
  • Minimum Audits: In addition to omitting all non-performance-related information (like in Reduced Audits), Minimum Audits mode will not generate a Long Task Timeline or the Third Party Tracking information.

Test information	Standard Mode	Reduced Audits	Minimum Audits
Performance Audits	✅ Yes	✅ Yes	✅ Yes
Accessibility Audits	✅ Yes	❌ No	❌ No
Best Practices Audits	✅ Yes	❌ No	❌ No
SEO Audits	✅ Yes	❌ No	❌ No
Third Party Audits	✅ Yes	✅ Yes	❌ No
Long Task Timeline	✅ Yes	✅ Yes	❌ No