Are my formulas safe?

Yes. Formulas, cell values, formatting and sheet structure are preserved exactly; only embedded raster images inside the package are re-encoded.

Does the workbook get uploaded?

No. The file is processed entirely in your browser — nothing is sent to any server, and nothing about your data is logged.

Why would an XLSX be huge?

Usually embedded pictures: pasted screenshots, product photos, logos at full resolution. Optimizing those is where the size wins come from.

Can it compress .xls or .csv files?

.xls (legacy binary) is not supported. For .csv, use the CSV tool — it can convert and gzip-compress your data.

Compress Excel workbooks — locally

Shrink heavy .xlsx workbooks by optimizing the embedded images inside the package. Formulas, cell styles and sheet data are left exactly as they are — the tool rebuilds the package around them, in your browser.

Open the XLSX compressor tool Runs entirely in your browser — files never leave your device.

What this tool does

Like DOCX, an .xlsx file is a ZIP package. When a workbook contains screenshots, logos or pasted images, those assets dominate the file size. The tool re-encodes them and rebuilds the package with worksheet XML, formulas and styles untouched.

Workbooks that are mostly data may barely shrink — spreadsheets are already compact, and the tool reports the honest measured outcome rather than a fake percentage.

How to compress an XLSX without uploading it

Drop in the workbook. Add your .xlsx file to the home-page tool.
Optimize the package. Embedded images are re-encoded and the package is rebuilt — locally.
Save the result. Download the smaller workbook and open it in Excel as normal.

Supported operations

This list is generated from CompressKit's capability registry — only implemented and tested operations appear here.

Optimize the file package

Optimize embedded images and rebuild the XLSX package, leaving formulas and styles untouched.
Inspect file details

See package composition and sizes before optimizing.

Frequently asked questions

Are my formulas safe?: Yes. Formulas, cell values, formatting and sheet structure are preserved exactly; only embedded raster images inside the package are re-encoded.
Does the workbook get uploaded?: No. The file is processed entirely in your browser — nothing is sent to any server, and nothing about your data is logged.
Why would an XLSX be huge?: Usually embedded pictures: pasted screenshots, product photos, logos at full resolution. Optimizing those is where the size wins come from.
Can it compress .xls or .csv files?: .xls (legacy binary) is not supported. For .csv, use the CSV tool — it can convert and gzip-compress your data.

Ready to try it?

The XLSX 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 XLSX compressor tool