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Merge CSV Files

Combine two CSV files with matching headers.

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Your inputs are processed locally. Review the method and limitations before relying on the estimate.

Upload a CSV file (maximum 3 MB) or paste its text below. Nothing is transmitted to our server. For spreadsheet CSV exports, formula defense may change raw cell text; use JSON when exact data preservation is essential.

Browser processing is bounded to 3 MB per file and at most 15,000 parsed CSV rows. Download the output to keep a copy; nothing is saved here.

Worked example

Two CSVs with identical headers become one with a single header row.

Frequently asked questions

Are my files uploaded?

No. Files are read by JavaScript in this browser; no server processing or background upload is used.

Are spreadsheet formulas executed?

No. Input is treated as plain text. CSV export applies defense-in-depth spreadsheet formula escaping, which can change the literal exported cell value.