Check the whole gallery, not one image
Screenshot set checker
A listing gallery is read as a set. One dark screenshot among light ones, a different aspect ratio or a near-duplicate looks careless even when each image is fine alone. Drop your screenshots here and the page reads size, ratio, file size and type, compares the images with each other, and gives you an order and a Markdown block to paste.
Everything runs in your browser. Files are decoded locally and never uploaded, and nothing is stored. This tool checks a set; to resize one image for a listing field, use the listing image preparer.
How to use it
- Add your screenshots. Choose up to 10 PNG, JPEG, WebP, GIF or AVIF files in the order you would like to show them.
- Reorder the gallery. Use Move up and Move down on each card until the story reads in the right order, and remove any you do not want.
- Read the flags. Work through Fix items first, then Check items. Cards with a problem get an amber border so you can find them.
- Copy the Markdown. Take the listing-ready order and the Markdown block, then replace each ALT TEXT placeholder with a plain sentence describing the screen.
What is measured and how
Dimensions and file size come from the decoded image and the file itself. The aspect ratio is reduced and matched to a common name (16:9, 16:10, 3:2, 4:3, 1:1, 3:4, 9:16) when it is within 1.5 percent, otherwise shown as a fraction. A set is flagged when the ratios differ, and the odd ones are named.
Theme is judged from the mean brightness of a 64 by 64 downsample, weighting red, green and blue by the standard relative luminance coefficients from the sRGB specification. Below 100 of 255 counts as dark, above 150 as light, and in between as mid. A set is flagged when it contains both dark and light shots. This is a brightness estimate, not an understanding of the interface.
Duplicates use a difference hash (dHash): the image is reduced to a 9 by 8 grayscale grid and each of the 64 bits records whether a pixel is brighter than its right neighbour. Two images with a Hamming distance of 4 bits or fewer are reported as the same picture. It catches re-exports and small crops of the same screen; it can miss a heavily edited copy and can, rarely, match two very plain screens.
Thresholds are working limits: widths under 1280 px and files over 5 MB are flagged because small images look soft when scaled and many upload forms cap size. Common listing fields accept 16:9 or 4:3, but check the destination for its own rule. The order suggestion keeps your upload order, moves shots that match the majority ratio and theme first, and leaves out later duplicates.
Questions
Are my screenshots uploaded?
No. Files are read in your browser with the standard image and canvas features and never sent anywhere. Closing the tab discards everything.
What ratio should the screenshots be?
Common listing fields accept 16:9 or 4:3, so either is a safe starting point. Check the field you are filling in for its own rule, and keep every shot in the set at the same ratio.
Why does it say my light screenshots are mixed with dark ones?
The tool averages the brightness of each image. Below 100 of 255 reads as dark and above 150 as light. A dark editor next to a white dashboard is flagged so you can decide if the mix is intentional.
How does it find duplicates?
It computes a 64 bit difference hash for each image and compares them. Images within 4 bits of each other are called duplicates. That catches the same screen exported twice, not two different screens that happen to look alike.
Why 1280 pixels wide?
It is a working minimum: below it, screenshots tend to look soft once a listing page scales them to fit. It is a guide, not a platform rule.
Can I resize images here?
No, this tool only checks a set. To crop or resize one image for a listing field, use the listing image preparer.