Office Open XML Spreadsheet (XLSX) stores cell values, formulas, formatting, and charts as zipped XML, the default format for Microsoft Excel 2007 and later. FB2 file (FB2) stores data in the FB2 format. 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. The result is a standard FB2 file readable by any compatible application. 1converter handles XLSX-to-FB2 conversion server-side: files are uploaded over HTTPS, processed on isolated cloud infrastructure, and the converted output is available for download for 24 hours before automatic deletion. No account is required for standard conversions.