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    SnapSiteScan

    SnapSiteScan verdict

    Your site is slow on mobile only

    When desktop passes and mobile fails, the files are not too large for your network — they are too demanding for the device, and the gap is almost always JavaScript execution.

    Ownership

    Front-end development

    This is a front-end problem, and it is invisible from a developer's laptop. It will keep being reported by users and denied internally until someone tests on a mid-range phone.

    What happens if you do nothing?

    The majority of your traffic is mobile, so the failing test is the one that represents most of your visitors — and it is the one Google uses to assess the page.

    Do this first

    1. 1

      Test on a real mid-range phone once

      One session on an average Android device replaces weeks of internal argument about whether the problem is real.

    2. 2

      Cut JavaScript, not bytes

      Phones parse and execute the same script several times slower than a laptop. Removing code helps far more than compressing it.

    3. 3

      Serve mobile-sized images to mobile devices

      Desktop-resolution images on a phone waste both bandwidth and decoding time, and decoding is the part people forget.

    4. 4

      Defer everything the first screen does not need

      Sliders, chat, tracking and animation libraries cost the most exactly where you can least afford them.

    How do you know this verdict is yours?

    • A large gap between the desktop and mobile score in the same scan.
    • Total Blocking Time is acceptable on desktop and poor on mobile.
    • Long main-thread tasks appear only in the mobile run.
    • The site feels fine on the office network and slow on a real phone.

    Not worth your time given this verdict

    • Optimising the desktop experience, which is already passing.
    • Hosting upgrades — the same server serves both tests.
    • A separate mobile site: it doubles the maintenance and rarely solves the execution cost.

    Deprioritising a finding is a prioritisation call, not a claim that it never matters.

    When to stop

    When should you stop working on this?

    Stop when the mobile score is within about ten points of desktop and Total Blocking Time on mobile is under 200 ms.

    Send this to your team

    The message that ends the discussion

    Desktop is fine, mobile is not. The difference is JavaScript execution on slower devices, not our server. We need to remove or defer scripts rather than upgrade hosting.

    Quick answer

    Why is my site fast on desktop but slow on mobile?

    When desktop passes and mobile fails, the files are not too large for your network — they are too demanding for the device, and the gap is almost always JavaScript execution. This is a front-end problem, and it is invisible from a developer's laptop. It will keep being reported by users and denied internally until someone tests on a mid-range phone.

    Owner
    Front-end development
    First action
    Test on a real mid-range phone once

    What to do next: One session on an average Android device replaces weeks of internal argument about whether the problem is real.

    Not sure which verdict is yours?

    Run a scan and SnapSiteScan will name the dominant cause, the owner and the first action for your page — using the same model as this page.

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