Merge CSV Files Learn more

Append two large CSV files into one. Handles massive files (100MB+) that crash Excel or Google Sheets. Streamed locally in your browser - nothing is uploaded.

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File 1 (primary) - header kept from this file

File 2 (append) - first row skipped by default

Skip header row from File 2 Add blank line between files

Merging... 0%

Merge Complete

Total Rows

Output Size

Time (sec)

Header Rows Skipped

Files are processed in streaming chunks - even 500MB+ CSVs work smoothly. Nothing leaves your browser.

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Merge CSV Files

What this solves

Merging huge CSV files (100MB, 500MB, even 1GB+) that crash Excel, Google Sheets, or other tools
Simple row append - File 1's data followed by File 2's data
Optionally skips the header row from File 2 to avoid duplicate headers

How it works

Select or drag-drop two CSV files
Click "Merge Files" to combine them
Files are streamed in chunks (not loaded entirely into memory)
Download the merged result as a single CSV

Privacy

Everything runs locally in your browser using the File API
No data is uploaded to any server