CSV Merger – Append Multiple CSV Files
Append multiple CSV files into one table with stack or union columns
Append two or more CSV files into one longer table. Stack mode uses the first file’s headers and places matching values beneath them; union mode keeps every unique header found across the files and fills missing fields with empty cells.
CSV Merger combines rows in upload order. It does not match records by ID or place columns side by side. For key-based matching, use the CSV Joiner listed below.
Drop your file here or browse from your device
Accepts CSV, TSV, TXT. Maximum input: 10 MiB. Files above this hard limit are rejected before local processing.
How to Use
- Upload the first CSV, then add each additional file in the order you want its rows appended
- Choose stack to use the first file’s headers or union to keep every header
- Preview the combined rows and columns
- Download the merged CSV
Features
- Stack rows using the first file’s column set
- Union every unique header across files
- Fill missing columns with empty cells
- Preserve the order in which files were added
- Preview the combined table before downloading
Use Cases
- Append monthly exports that share the same columns
- Recombine files created by a CSV splitting workflow
- Union vendor exports whose optional columns differ
Frequently Asked Questions
What if the files have different columns?
Merging works best when the files share a header row. When columns differ, check the preview before downloading — mismatched headers are the usual cause of values landing in the wrong column after a merge.
Is the header row repeated for every file?
No. One header row is written at the top of the merged output, and the data rows from each file follow it, which is what an import expects.
Is my data private when merging CSV files?
The files are read and merged in your browser and their contents are not sent to the app server. As with any website, avoid opening highly sensitive files on a device or browser you do not trust.
How are columns handled when merging?
Stack mode follows the first file’s headers and leaves out columns that only exist in later files. Union mode includes every unique header and fills missing values with empty cells.
Can I merge CSV files by an ID or email column?
CSV Merger only appends rows. Use CSV Joiner for key-based matching, side-by-side columns, and inner, left, right, or full outer joins.