Excel XLSX converter

XLSX is the modern Excel workbook format: a zipped Office Open XML package containing worksheets, shared strings, formulas, styles, drawings, charts, pivot caches, metadata, and relationships. It can hold many tables, or no clean table at all. A workbook may include title rows, merged headers, hidden sheets, formulas with cached results, comments, filters, charts, images, and data validation. Conversion is therefore a selection problem before it is a serialization problem. You must decide which sheet, which header row, and whether formulas should be exported as formulas or as the last calculated values stored in the file.

Variants change risk. XLSX is macro-free. XLSM adds VBA macros, which most safe converters preserve as files only when staying in Office formats and otherwise ignore or strip; they should never run during conversion. Legacy XLS is binary and has row, column, encoding, and date-system quirks. XLSB is binary workbook storage and can be faster in Excel but less broadly supported by web tools. ODS is an OpenDocument spreadsheet with a different formula language and style model. CSV is not a workbook variant at all; it is one delimited table with no formulas, sheets, charts, or styling.

XLSX is read and written by Excel, LibreOffice, Google Sheets exports, accounting packages, ERP systems, data labeling tools, survey platforms, BI products, and programming libraries such as SheetJS, openpyxl, pandas, and ExcelJS. Those producers differ in how reliably they store cached formula results, date serials, leading zeroes, and number formats. A cell displaying 00123 may actually be the number 123 with a custom format. A date may be a serial number using the 1900 or 1904 date system. A formula may be stale if the workbook was generated without recalculation.

Conversion gotchas center on losing workbook context. XLSX to CSV flattens one worksheet and drops formulas, styles, comments, charts, filters, frozen panes, and hidden data. XLSX to JSON must decide whether blank cells become empty strings, nulls, or missing keys. XLSX to PDF preserves the printed view but may depend on page setup, print areas, and fonts. XLSX to Markdown only works for rectangular tables. Before converting, open a sample, identify the authoritative sheet, remove explanatory rows above the header, confirm date and identifier handling, and compare row counts after export. Keep the workbook when audit trails, formulas, or multiple sheets matter.

For repeatable spreadsheet conversion, treat the workbook as a small database with presentation attached. Define sheet names, header rows, expected columns, date formats, decimal conventions, and allowable blank values. Convert a representative file first, then compare row counts, totals, and a few edge cells such as long IDs, negative currency values, and formulas that reference hidden sheets. If the workbook is a business control, archive the original beside any CSV, JSON, or SQL derivative. If it is a report for people, PDF may be a better conversion target than data formats because the visual layout is part of the meaning. For automated imports, fail loudly on unexpected sheets or columns and log warnings beside the converted file.

Official Excel XLSX specification