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Image check

Do4U checks the images of one page. You enter the address of the page. Do4U reads the page and each image on it and looks at the format, the file size and the pixels of the file, and at the HTML: width and height, loading, fetchpriority, srcset and sizes, picture sources and background images in style attributes. Do4U also guesses the likely LCP image, the largest image at the top of the page. You get a table of the images with the findings, the total weight and a short summary of the potential issues. No AI is used, and the check is free.

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Who it is for

For website owners, agencies and developers who want faster pages and fewer layout jumps, for example before a launch, after a redesign or when a page feels slow on a phone.

Typical uses

  • Find heavy images and images that are much larger than they are shown
  • Check that the large image at the top does not load lazily
  • Find images without width and height that make the page jump
  • See which JPEG and PNG files could be WebP or AVIF

Example

Input

https://example.com/

Result

#1 /img/hero.jpg – JPEG, 480 KB, 2400 × 1200 pixels, likely LCP image. Error: it has loading="lazy". Warning: heavy image (more than 200 KB). Hints: WebP or AVIF is often smaller; no srcset. #2 /img/team.png – PNG, 90 KB, 640 × 480 pixels. Warning: no width and height, the page can jump. Hint: WebP or AVIF is often smaller. #3 /img/logo.svg – SVG, 2 KB. No problems found. Total weight of the images read: 572 KB (3 files).

A fixed example, shortened. Real results are AI-generated: please check them.

Price and limits

Price
free, without sign-up
Available with
Free, With package
Input limit
One page with up to 300,000 characters of HTML

Privacy

Processed on our own servers in the EU (Poland). Inputs and results are deleted after 7 days (Free) or 30 days (packages), or right after you see the result if you choose not to store them. Images are deleted right after processing.

In the API

Tool name: image_performance_check. Create a job with POST /api/v1/jobs and fetch the result with GET /api/v1/jobs/{id}. You find your API key in your account.

curl -X POST https://do4u.eu/api/v1/jobs \
  -H "Authorization: Bearer d4u_…" -H "Content-Type: application/json" \
  -d '{"tool": "image_performance_check", "url": "https://example.com/"}'

Full API documentation →

Questions and answers

Does the image check use AI?

No. Do4U reads the page and the images, and the code checks them. The format and the pixels come from the first bytes of each file. The check is free; each account has a limit of checks per day.

How does Do4U know the LCP image?

It does not measure it. It guesses from the HTML: an image with fetchpriority="high", or else the first large image in the main content. The browser decides the real LCP element, so check it with the performance tools of your browser.

Why does a size say "at least"?

Do4U reads each image only up to a limit. A larger file is shown with the size read so far. It is then certainly heavy. Some servers send WebP or AVIF only to browsers that ask for it, so the format can differ in your browser.

Is my text stored?

Only as long as needed: 7 days on Free, 30 days with a package – or not at all if you choose not to store it. Processing happens on our own servers in the EU (Poland).

Can I use the result right away?

Results are AI-generated. Please read them before you publish or send them.

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