Local by design. Files are decoded, resized, encoded, compared, and exported in this browser. The application contains no upload endpoint, analytics call, database, or server-side image processing.

Validation. Files are checked by MIME type and basic binary signature. Raster limits are enforced before processing. Animated PNG/WebP are rejected so the app does not silently flatten animation into a single frame.

Quality claim. No lossy compressor can guarantee literally zero quality loss. Visual Lossless therefore searches for a small file inside a strict visual-difference budget. PNG lossless mode preserves pixels. The Never Make the File Larger safeguard prevents a conversion such as JPEG → PNG from being reported as a compression win.

Optional free enhancement. UPNG.js + Pako are used as browser-side PNG optimization/Deflate resources when their pinned CDN scripts are available and the option is enabled. It can perform lossless PNG encoding or color-quantized PNG minification.

TinyPNG-style workflow reference. The interface follows the same practical pattern of dropping a batch into a queue, inspecting savings, and downloading optimized files, while this app intentionally keeps processing local. TinyPNG currently supports batch upload, WebP/JPEG/PNG/AVIF/JXL workflows, and its documentation describes smart lossy compression with very low visible differences.