### Simulation Configuration

Illustrative simulation only: no website or images are loaded, no network is throttled, and CPU and memory values are synthetic-not measurements of your device or site.

Number of Images

20

Network Profile

Start Test

### Simulated Metrics

Summary  Timeline

0

Simulated Images

0.0s

Simulated Timeline

0%

Synthetic CPU Value

0%

Synthetic Memory Value

# Lazy Load Tester - Illustrative Loading Simulation

Explore a synthetic loading timeline; this page does not test a real website or measure network, CPU or memory.

## Key Features

#### Network Simulation

Test with 3G, 4G, 5G, and WiFi profiles

#### Performance Metrics

Synthetic CPU, memory and timeline values, not device measurements

#### Timeline Analysis

Detailed loading timeline and metrics

#### Export Data

Download metrics as JSON for analysis

## What is Lazy Load Tester?

Lazy Load Tester illustrates a synthetic loading timeline using assumed profiles. It does not load a real page, throttle your connection, observe images or measure CPU and memory. For actionable website results, use a real browser audit and inspect actual loading behavior.

For another illustrative model, try the [Lighthouse Score Simulator](https://www.toolcomb.com/lighthouse-simulator). It also does not audit a live page. Use your browser's network panel to inspect actual image requests and compare the results with a real performance audit.

### How to Use

1. Set the number of images to test (5-100)
2. Select a network profile or create a custom one
3. Click "Start Test" to begin the simulation
4. Review the simulated timeline and values
5. Export the results for detailed analysis

### Network Profiles

#### 3G

0.4 Mbps download. Simulates slow mobile networks with high latency.

#### 4G LTE

10 Mbps download. Typical mobile network speed with moderate latency.

#### 5G

100 Mbps download. Fast mobile network with low latency.

#### WiFi

50 Mbps download. Typical home/office WiFi speeds.

### Frequently Asked Questions

#### What is lazy loading?

Lazy loading defers loading images until they're needed, improving initial page load performance.

#### How does Intersection Observer work?

Intersection Observer detects when elements enter the viewport and triggers loading at that moment.

#### What network speeds should I test?

Test with 3G, 4G, and WiFi to understand performance across different user conditions.

#### What are good performance targets?

Core Web Vitals include LCP, INP and CLS, but this simulation does not measure them. Use field data and a real browser audit for your site.

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### Related guides

Read the how-to, then come back to this tool when you are ready to run it locally.

- [How Lazy Loading Images Affects Page Speed Lazy-load vs LCP trade-offs, with a browser tester for your markup.](https://www.toolcomb.com/blog/how-lazy-loading-images-affects-page-speed)

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