Lighthouse scores can vary 5-10 points between runs due to network conditions, CPU load, and browser state. These techniques improve consistency for reliable Core Web Vitals measurement.

Why Scores Vary

Single Lighthouse runs can fluctuate by 5-10 points due to:

• CPU load from other browser tabs or processes
• Network latency variations
• Memory pressure
• Background service workers

For reliable performance monitoring, use multiple samples.

Multiple Samples Per URL

Run Lighthouse multiple times and average the results for better accuracy:

import { defineUnlighthouseConfig } from 'unlighthouse/config'

export default defineUnlighthouseConfig({
  scanner: {
    samples: 3, // Run 3 scans per URL and average results
  },
})

Reduce Parallel Scans

Limit concurrent workers to reduce CPU contention and improve score consistency:

import { defineUnlighthouseConfig } from 'unlighthouse/config'

export default defineUnlighthouseConfig({
  puppeteerClusterOptions: {
    maxConcurrency: 1, // Single worker for maximum accuracy
  },
})

Enable Throttling

Network throttling simulates real-world conditions and reduces score variability:

export default defineUnlighthouseConfig({
  scanner: {
    throttle: true, // Simulate 4G network
  },
})

Recommended Production Config

For the most accurate results:

export default defineUnlighthouseConfig({
  scanner: {
    samples: 5,
    throttle: true,
  },
  puppeteerClusterOptions: {
    maxConcurrency: 1,
  },
})