CSV Merger
Merge several CSV files into one. Match columns by header name in any order, choose strict or union-of-headers mode, add a source-file column and download one CSV.
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About the CSV Merger
CSV Merger stacks several CSV files into one file with a single header row. Columns are matched by header name, so files with the same columns in a different order still line up.
Strict mode requires every file to have the same columns; union mode keeps every column from every file and fills missing cells with blanks. Duplicate or blank headers are shown before merging, header matching can ignore letter case, and an optional column records which file each row came from.
How to use
- Add two or more CSV files.
- Reorder the files with the arrow buttons.
- Choose strict or union mode and the matching options.
- Review the combined columns, row count and any header conflicts.
- Click Download merged CSV.
Key features
- Multiple files with visible, reorderable order.
- Header-name matching regardless of column order.
- Strict mode or union of headers with blank filling.
- Optional case-insensitive matching.
- Optional source filename column.
- Duplicate and blank header conflicts shown before merging.
Best practices
- Use strict mode when files must share a schema.
- Add the source column when you may need to trace rows back.
- Check the combined schema preview before downloading.
Benefits
- One file instead of many monthly exports.
- No copy-paste mistakes when column orders differ.
- Private: files never leave your device.
Frequently asked questions
What if a file has an extra column?
Strict mode stops and lists the difference. Union mode adds the column and leaves it blank for rows from files that do not have it.
How are duplicate headers handled?
Within a file, a repeated header is renamed (e.g. “Amount (2)”) and shown as a conflict so you can check how it will be matched.
Do the files need the same delimiter?
No. Each file’s delimiter is detected separately; the merged file uses the delimiter you choose.
Is my data uploaded?
No. Files and pasted data are processed only in your browser. Nothing is uploaded or stored, and the tool keeps working offline once the page has loaded.