Merge CSV Online

Switch to the Combine & Stack tab, upload or drag multiple CSV files, review the detected headers and row counts, choose your options, then click Merge. A combined CSV file will be ready to download immediately.

Yes. The Combine & Stack mode matches columns by header name so files with different column orders are aligned automatically. Columns that only appear in some files are included with empty values for the other rows.

Yes. Use the Deduplicate & Condense tab to remove exact duplicate rows or merge rows that share the same composite key before downloading.

Yes. In the Combine & Stack tab, enable the Add source filename column option to add a source_file column to the merged output showing the original file name for each row.

Combine & Stack appends rows from multiple files vertically into one output, matching columns by header name. Join by Key Column matches rows from exactly two files side by side using a shared key field such as id, email, or order_number. Use Stack for combining similar data files; use Join when you need to enrich one file with data from another.

No. All CSV processing runs locally in your browser using JavaScript. No files are uploaded to any server, and no account is required.

Upload your files in the Combine & Stack tab and expand the Header Analysis panel before merging. It shows which columns are shared across all files and which are only in some files, so you can check for issues before downloading.

Because the tool runs in the browser, performance depends on your device and browser memory. For very large files, consider splitting them into smaller batches first using Split CSV Online, then merging the results.