Why does Google use mobile-first indexing?

Google switched to mobile-first indexing because the majority of global web traffic now comes from mobile devices. Using the mobile version of a page to determine rankings better reflects the experience of most users.

How is mobile speed testing different from desktop?

Mobile tests simulate a mid-range mobile device with a slower CPU (4x CPU throttle) and a slower network connection (4G / 10Mbps). This represents the real-world conditions for a typical mobile user.

My site looks fast on mobile but the score is low — why?

Perceived speed on a fast phone on Wi-Fi can differ significantly from the test conditions (mid-range device, 4G network). Lighthouse measures the experience for the median mobile user, not the ideal case of a high-end phone on a fast connection.

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Mobile Website Speed Test

Google ranks your website based on its mobile performance. More than 60% of web traffic is on mobile. FixTools tests your website specifically under mobile conditions — slower CPU, slower connection — giving you the score that actually matters for SEO.

⚡ Use Tool Now How it works

Cost: Free forever
Sign-up: Not required
Processing: In your browser
Privacy: Files stay local

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Mobile device emulation (4G, typical Android CPU)

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Mobile Core Web Vitals scoring

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Mobile-specific recommendations

Web Tool

Website Speed Test

All processing happens in your browser — your files are never uploaded to any server.

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100% Free · No account · Works on any device

How to use this tool

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Test your URL under mobile conditions — Google's standard for mobile-first indexing.

How It Works

Step-by-step guide to mobile website speed test:

1
Select mobile test mode
Choose mobile in the test settings to simulate a mid-range Android device on a 4G connection — Google's standard for Core Web Vitals measurement.
2
Run the test
Enter your URL and run the test. Allow extra time compared to desktop — mobile simulation takes slightly longer.
3
Review mobile-specific metrics
Check LCP under mobile conditions (target under 2.5s), TBT (target under 300ms), and CLS (target under 0.1).
4
Focus on mobile-specific improvements
Prioritise responsive images, JavaScript reduction, and eliminating render-blocking resources — these have the highest impact on mobile performance specifically.

Real-world examples

Common situations where this approach makes a real difference:

Mobile SEO audit

An SEO specialist runs mobile speed tests on a client's top 10 landing pages before presenting recommendations. 7 of 10 pages score under 50 on mobile due to large image files and render-blocking scripts — providing a clear, high-priority action list.

AMP migration decision

A news publisher considering an AMP implementation tests their current mobile performance. Scores above 75 suggest that mobile speed is not a critical issue and AMP's complexity may not justify the investment.

Developer mobile performance regression testing

A developer runs mobile speed tests after each sprint to catch performance regressions before they reach production. A score drop from 82 to 64 in one sprint immediately triggers investigation of what changed.

When to use this guide

Use this for any website you want to rank in Google, especially for mobile-heavy audiences. Mobile speed is the primary factor in Google's Page Experience ranking signal.

Pro tips

Get better results with these expert suggestions:

Mobile scores are always lower than desktop — this is normal

Mobile tests simulate slower CPUs and connections. A score of 70–80 on mobile may represent genuinely good performance. Aim for 80+ on mobile; achieving 90+ on mobile usually means your desktop score is excellent.

Responsive images are the most impactful mobile optimisation

Serving oversized desktop images to mobile devices is the single biggest waste of mobile bandwidth. Implement srcset or next-gen image formats (WebP, AVIF) to serve correctly-sized images for each screen.

Reduce JavaScript for mobile users

JavaScript parsing is far slower on mobile CPUs. Reducing JavaScript bundle size and deferring non-critical scripts has a disproportionate positive impact on mobile performance versus desktop.