RenameNinja is a native macOS application for batch renaming files by combining regular expressions to extract fields from original filenames and custom JavaScript code to transform those fields. The tool automatically extracts advanced metadata from images, audio files, videos, PDF documents, and Office files, making a wide range of variables available for use in renaming logic. The application offers an unlimited trial period with no functional restrictions, requiring a license only to remove periodic reminders. It is built entirely with SwiftUI and AppKit, ensuring deep integration with macOS starting from version Sonoma (14).