Modernize legacy XLS spreadsheets — locally, in your browser
Legacy .xls files are bloated and increasingly unsupported. Convert them to modern .xlsx (or CSV) locally — with clear warnings about what a converter cannot carry.
What this tool does
The converter reads the legacy BIFF format with SheetJS Community Edition and writes a fresh .xlsx package. Cell values survive; VBA macros, charts, embedded images and most formatting do not — every conversion warns you precisely what was dropped.
Password-protected workbooks are detected and rejected rather than bypassed, and the whole conversion runs in your browser’s worker.
How to convert a legacy .xls file without uploading it
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Add the file. Drop your .xls into the home-page tool.
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Choose .xlsx or CSV. Modernize to .xlsx (all sheets) or export the first sheet as CSV.
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Download locally. The converted workbook is saved straight back to your disk.
Supported operations
This list is generated from CompressKit's capability registry — only implemented and tested operations appear here.
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Convert format
XLS→XLSX modernize or CSV/TSV/TXT export (first sheet for text formats).
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Inspect file details
Sheet names, used ranges, row/column and cell counts.
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Reduce file size
Convert to a modern, compressed .xlsx package.
Frequently asked questions
- Is my spreadsheet uploaded anywhere?
- No. The conversion runs entirely in your browser.
- Why do my macros stop working?
- The converter cannot carry VBA projects. It tells you this explicitly on every conversion instead of silently dropping them.
- Are my formulas preserved?
- Computed values are preserved; formula definitions are not reliably carried by this converter. If your workbook depends on live formulas, keep the original .xls.
Ready to try it?
The XLS compressor tool runs on this site with no upload step — your file is processed by your own browser and saved back to your device.
Open the XLS compressor tool