Free CSV tool
How to convert an XLSX file to CSV
Most messy data actually arrives as Excel, not CSV. Columnwise reads .xlsx/.xls workbooks directly in your browser (via SheetJS), lets you pick which sheet if there's more than one, and exports whatever you build as clean CSV â no Excel install, no upload.
Runs entirely in your browser â your workbook stays on your machine.
How it works
- Drop in your .xlsx or .xls file the same way you'd add a CSV â same file picker, same drag-and-drop zone.
- Pick a sheet if the workbook has more than one â each sheet you select becomes its own source, named "workbook.xlsx â SheetName."
- Check the detected columns and types â Columnwise skips leading blank rows automatically before treating a row as the header, a common pattern in real spreadsheets.
- Build whatever pipeline you need (or none at all) â derive, join, aggregate â all optional.
- Export as CSV from the export panel once you're happy with the result.
Worked example
A workbook with a title row above the real header
A common Excel export pattern: row 1 is a report title or blank, row 2 is blank, and the real header starts at row 3. Columnwise detects this â it scans for the first row that has any non-empty cell and treats that as the header, rather than blindly assuming row 1 is always it. Merged cells and cells left blank by a merge come through as empty values, handled the same way a blank CSV cell would be.
Your workbook never leaves your computer
SheetJS parses the file entirely client-side â it's loaded on demand (only when you actually open an .xlsx file, so it doesn't slow down anyone using CSV) but never sends the file anywhere. Same guarantee as every other free tool here: open DevTools' Network tab and verify it yourself â the only request you might see at all is a Google Analytics page-view ping, if you've accepted analytics, and that never carries your file either.