Free visual diff tool

How it works

Upload two PNG or JPEG screenshots and we will compare them using SSIM (Structural Similarity Index) perceptual comparison. Unlike raw pixel diffing, SSIM evaluates structural, luminance, and contrast changes the way the human visual system does. This means fewer false positives from sub-pixel font rendering differences or minor anti-aliasing variations across environments.

Understanding the results

• Diff percentage — the proportion of the image that has changed, by area. A diff of 0% means the images are identical. A diff above 1% typically indicates a visible change.
• SSIM score — a value between 0 and 1. A score of 1.0 means the images are perceptually identical. Scores above 0.99 are generally considered a pass for visual regression testing.
• Diff overlay — highlighted regions show exactly where the two images differ. Red areas indicate pixels that have changed between the before and after images.

When to use this tool

Use the free diff tool for one-off comparisons: before and after a CSS refactor, checking a deploy, or reviewing a design change. For automated regression testing with baseline management, scheduled monitoring, and alerts, create a free account.