XLSX is a spreadsheet format: it stores cell values, formulas, formatting, and charts as zipped XML, the default format for Microsoft Excel 2007 and later. MOBI is a ebook format that stores reflowable text in the Mobipocket format originally designed for Amazon Kindle devices, now largely superseded by KFX. This conversion changes the file's encoding, compression method, and supported feature set. Metadata such as creation date and embedded colour profiles is preserved where the target format supports it. Converting between these two formats is common when the source application does not support MOBI natively or when the target platform only accepts MOBI. 1converter processes this conversion server-side using open-source tools. Files are transferred over HTTPS, converted on secure cloud servers, and automatically deleted after 24 hours.