RUM Monitoring

Real User Monitoring (RUM) collects performance data from actual visitors to your website. Unlike synthetic tests that run in controlled environments, RUM shows you how real users experience your site across different devices, networks, and locations.

What is RUM?

RUM captures browser-based metrics as users interact with your website:

• Performance metrics from the browser's Performance API
• Core Web Vitals as defined by Google
• User engagement like scroll depth and time on page
• JavaScript errors that affect user experience

Core Web Vitals

VitalSentinel tracks all Core Web Vitals metrics:

LCP (Largest Contentful Paint)

Measures loading performance - how quickly the largest visible element loads.

Common causes of poor LCP:

• Slow server response times
• Render-blocking JavaScript/CSS
• Large images without optimization
• Client-side rendering delays

CLS (Cumulative Layout Shift)

Measures visual stability - how much the page layout shifts unexpectedly.

Common causes of poor CLS:

• Images without dimensions
• Ads or embeds without reserved space
• Dynamically injected content
• Web fonts causing text shift

INP (Interaction to Next Paint)

Measures responsiveness - how quickly the page responds to user interactions.

Common causes of poor INP:

• Long JavaScript tasks blocking the main thread
• Heavy event handlers
• Large DOM size
• Third-party scripts

TTFB (Time to First Byte)

Measures server responsiveness - time from request to first byte of response.

Common causes of poor TTFB:

• Slow server processing
• No CDN or caching
• Database query delays
• Geographic distance to server

FCP (First Contentful Paint)

Measures initial render - when the first content appears on screen.

Using the RUM Dashboard

Overview

The RUM overview page shows:

• Overall Web Vitals scores (Pass/Fail)
• Trends over your selected time period
• Mobile vs Desktop breakdown
• Top pages by traffic

Percentile Values

VitalSentinel displays the 75th percentile (P75) value for each metric. This means 75% of your users experience this value or better.

The P75 is the industry standard for Core Web Vitals assessment and is what Google uses for search ranking evaluation.

Metric Detail Pages

Click on any metric to see detailed analysis:

• Distribution chart - Shows how users are distributed across good/needs improvement/poor
• Trend over time - Track improvements or regressions
• Breakdown by device - Compare mobile vs desktop
• Top pages - Which pages have the worst scores

Engagement Metrics

When engagement tracking is enabled, VitalSentinel also captures:

Scroll Depth

Track how far users scroll:

• 25%, 50%, 75%, 90%, 100% milestones
• Average scroll depth per page
• Correlation with content length

Time on Page

• Total time on page
• Active time (user is interacting)
• Idle time (user is not focused)

Page Views

• Total page views
• Unique visitors
• Pages per session

Error Tracking

RUM automatically captures JavaScript errors:

• Error message and type
• Stack trace for debugging
• URL where the error occurred
• Browser and device information
• Frequency of each error

Access errors in your domain's RUM Monitoring → Errors section.

Data Interpretation

Sample Rate

By default, 100% of visitors are tracked. For high-traffic sites, you can reduce this:

• data-sample-rate="0.5" tracks 50% of visitors
• data-sample-rate="0.1" tracks 10% of visitors

Lower sample rates reduce data costs while maintaining statistical significance.

Mobile vs Desktop

Core Web Vitals are measured separately for mobile and desktop:

• Mobile devices typically have slower connections
• Mobile CPUs are less powerful
• Google uses mobile metrics for search ranking

Geographic Variance

Performance varies by location due to:

• Distance to servers
• Network infrastructure quality
• Device prevalence

Best Practices

Improving LCP

1. Optimize and compress images
2. Use a CDN for static assets
3. Preload critical resources
4. Minimize render-blocking resources

Improving CLS

1. Always include width/height on images
2. Reserve space for ads and embeds
3. Avoid inserting content above existing content
4. Use CSS containment

Improving INP

1. Break up long JavaScript tasks
2. Use web workers for heavy processing
3. Debounce input handlers
4. Minimize main thread work

Improving TTFB

1. Use a CDN
2. Enable caching
3. Optimize database queries
4. Use HTTP/2 or HTTP/3

Related Features