Frequently Asked Questions

Yes, really. You can verify it yourself:

1. Open your browser's DevTools (F12)
2. Go to the "Network" tab
3. Upload files and merge them
4. You will see that there are NO POST requests to external servers with your data

All processing uses JavaScript running in your browser. Your files never leave your computer. If you disconnect Wi-Fi after loading the page, the tool will continue to work.

Only basic Google Analytics data (pages visited, country, browser). We have NO way of knowing:

• Which files you merged
• How many files
• The content of your data
• File names

It is impossible for us to know because nothing ever reaches our server.

Yes, it is safe. In fact, that was the reason I created MergeExcel — I needed to merge files containing sensitive client data and did not want to upload them to unknown online tools.

That said, I always recommend:

• Use HTTPS (the padlock should be green in your browser)
• If you work at a company with strict security policies, check with IT first
• For extremely sensitive files, consider using the tool offline (by downloading the page)

Work very well:

• .xlsx (Excel 2007 and later) ✅
• .xls (Excel 97-2003) ✅
• .csv (comma-separated values) ✅
• .xlsm (Excel with macros — macros are not preserved) ⚠️

Experimental support:

• .ods (OpenOffice/LibreOffice) — works but formatting may vary
• .tsv, .txt — interpreted as CSV

NOT supported:

• .dbf — promised but the library has known bugs
• .xml — only specific SpreadsheetML

It depends on the merge mode:

• "Separate Sheets": Yes, formulas and basic formatting (colors, bold, etc.) are preserved.
• "Append Rows" / "Combine Columns": Only values are kept. Formulas are converted to their results.

Known limitations:

• Charts and images are NOT copied
• Complex formatting (custom borders, data validations) may be lost
• VBA macros are not preserved

Technical limits:

• 50 MB per individual file
• 200 MB total (all files combined)

Practical limit (browser memory):

• ~10–15 MB works perfectly on any computer
• 15–50 MB works, but may be slow on older machines
• Over 50 MB: your browser may run out of memory and crash

If you have very large files (>50 MB), we recommend using Python with pandas or Excel desktop with Power Query.

There is no technical limit on the number of files, but:

• 2–10 files: perfect, fast
• 10–50 files: works, but takes longer
• 50+ files: possible, but consider whether automating with Python might be better

The real limit is the total size (200 MB) and your browser's memory.

Common causes:

1. Files too large — The browser ran out of memory. Try fewer files or smaller files.
2. Corrupt file — If one of your Excel files is damaged, it can block the process. Try merging files two at a time to identify which one is causing the problem.
3. Outdated browser — MergeExcel requires modern JavaScript. Update your browser.

Quick fix: Refresh the page (F5) and try with fewer files.

Try this:

1. Make sure the downloaded file has the .xlsx extension
2. Try opening it with Google Sheets instead of Excel — there are occasional compatibility issues
3. If you used "Combine Columns" with many files, the result may be too wide for Excel (limit of 16,384 columns)

If the problem persists, write to me at hola@mergeexcel.es with details.

Check the following:

• Did you have "Skip empty rows" enabled? That removes completely blank rows.
• Did the original files have all the rows? Sometimes Excel hides rows that are still there.
• Did you use "Include headers from first file only"? That skips the first row of all subsequent files.

Recommendation: Always review the merged file before deleting the originals. Use the preview before downloading.

Technically yes, but:

• iOS/iPad: Works, but Safari has limitations with file selection. It is better to use Chrome or Firefox on iOS.
• Android: Works well on Chrome, Firefox, and Edge.

Limitation: On mobile devices with low RAM (<4 GB), large files may crash the browser. We recommend using MergeExcel on a computer for files >10 MB.

Use Power Query if:

• You need complex merges (joins, filters, transformations)
• You work with very large files (>100 MB)
• You need to automate with periodic updates

Use MergeExcel if:

• You just need to stack or combine files quickly
• You don't have Excel installed (Mac, Linux, Chromebook)
• You want to get it done without learning Power Query (which has a learning curve)
• You need total privacy (without files leaving your PC)

MergeExcel is simpler and faster for 80% of use cases. Power Query is more powerful for the advanced 20%.

The JavaScript is completely visible (right-click → View Page Source). There is no obfuscation or tricks.

It is currently NOT on GitHub as a public repository, but the code is auditable in the browser. If there is enough interest, we may publish it on GitHub.

It is 100% free. There is no premium version, no artificial limits, no "7-day trial".

Google AdSense ads help cover hosting costs (~10€/month). If you use an ad blocker, no problem — the tool works just the same.

Yes, you can use it freely. No commercial license is required.

Recommendation: If your company has strict security policies, show them this FAQ and have IT review the code. Some security departments prefer to deploy tools internally.

If you need an on-premise version (installed on your own server), contact me at: hola@mergeexcel.es