CSV Merge Tool
Combine Multiple CSV Files into One

Frequently Asked Questions

How do I use this tool?

Drag and drop multiple CSV files onto the drop zone, or click to browse. Review the file list, then click "Merge Files". Once merging is complete, preview the result and download the CSV file.

Can I merge CSV files with different columns?

Yes. This tool uses DuckDB UNION BY NAME, which aligns columns by name. Missing columns in some files are filled with NULL values in the merged output.

Is there a limit on how many files I can merge?

There is no hard limit on the number of files. However, each file can be up to 500MB, and the total size of all files combined must be under 1GB to stay within browser memory limits.

Is my data uploaded to a server?

No. Your files never leave your browser. All processing happens locally using WebAssembly. No data is sent to any server.

What browsers are supported?

Any modern browser that supports WebAssembly: Chrome, Firefox, Edge, Safari (14+). Chrome is recommended for best performance with large files.

Is it free?

Yes, this tool is completely free with no file count or row limits.

Can I merge CSV files with different encodings (e.g. UTF-8 and Shift_JIS)?

Yes. Each file's encoding is automatically detected before merging. Non-UTF-8 files (such as Shift_JIS, EUC-JP, or ISO-8859-1) are converted to UTF-8 internally, so the merged output is always a clean UTF-8 CSV regardless of the original encodings.