CSV or Excel tool
Merge CSV
Stack several CSV files into one. Keep the files in the same column order for a quick append, or combine columns when the headers differ.
Add files
Drop CSV files here, or choose files. Everything stays on this device.
Waiting for files
Accepted input
- Two or more CSV or TSV files
Limits
- Up to 20 MB per CSV/Excel file and up to 100000 rows.
- CSV, TSV, XLSX and JSON inputs are supported in this category.
Local processing
- Files are read in your browser and are never uploaded to a server.
- Nothing is stored after you close or reload the page.
How to use Merge CSV
- Add two or more CSV files with the drop zone or the file chooser.
- Reorder the list so the rows appear in the order you need.
- Choose Same headers or Union columns, then press Merge CSV files.
What it does
- Reorders files before merging so the output row order is what you arranged.
- Same-headers mode refuses mismatched columns instead of silently mixing data.
- Union mode aligns columns by name and fills gaps with empty cells.
Limits and things to know
- The first file in the list defines the header order in union mode.
- There is no de-duplication; identical rows appear once per input file.
- Each input must stay within the per-file and total size limits.
Example
Appending monthly exports
Add january.csv, february.csv and march.csv, all with id,name,amount. Keep Same headers and merge to get one file with the three months of rows in that order.
Frequently asked questions
What if the files have different columns?
Same-headers mode reports the mismatch and stops. Switch to Union columns to align by name, filling missing values with empty cells.
Which header order is used?
In union mode the order is the first file's columns followed by any new columns from later files.
Are duplicate rows removed?
No. Merging keeps every row. Use Remove CSV Duplicates on the result if you need to de-duplicate.
Runs entirely in your browser on ap98.com. Files are never uploaded.