Files
Merged preview
When you need to combine the monthly CSV from each branch, a form export split across several files, or daily CSVs a tool keeps spitting out, this merges them into one file in your browser — no command-line batch, no Excel macro, no install. Click "Add CSV files" to pick several, or drop them all onto the page, and it shows the merged result as a table preview in the order you added them. Merging isn't a blind row-by-row concatenation: it treats the first row of each file as the header and lines columns up by name. Even if files have columns in a different order, same-named columns align; a column that exists in only some files is added as part of the union, and rows that lack it are left blank — so mixing an older CSV with a newer one whose columns changed still works. Turn on "Remove duplicate rows" to keep only one copy of identical rows (the number removed is shown), handy for de-duping a contact list or cleaning up a double export. Turn on "Add source filename column" to append a column recording which file each row came from. The default "Save as" is "UTF-8 with BOM (Excel)" so it opens cleanly in Excel. Under the hood, reading the files, detecting their encoding (UTF-8 or Shift_JIS automatically), merging, and writing all happen inside your browser in JavaScript, so your files are never uploaded, stored, or sent to a server — safe for customer lists, sales figures, or internal data you'd rather not put on a cloud merger (and for workplaces where uploading files externally is against policy). Want to inspect a CSV as a table first? Try csv-viewer; to fix a garbled file, csv-encoding; to turn an .xlsx into CSV, excel-csv.
How to use
- Click "Add CSV files" to pick several, or drag and drop them all onto the page (no command line, script, or app needed). The merged result shows as a table preview in the order added.
- Optionally turn on "Remove duplicate rows" and "Add source filename column". The first row of each file is treated as the header and columns are matched by name, so a different column order still lines up.
- Pick a "Save as" encoding (UTF-8 with BOM is the default for Excel) and click "Download CSV" to save one merged.csv. Your files are never uploaded.
FAQ
Can I merge CSVs whose columns are in a different order or count?
Yes. The first row of each file is treated as its header, and columns are matched by name, so a different order still lines up correctly. A column that exists in only some files is added as part of the union, and rows that don't have it are left blank — so it holds up even when an older and a newer CSV have different columns. (If instead you want to stack everything as data without treating the first row as a header, that's a slightly different use case.)
Can it remove duplicate rows?
Yes. Turn on "Remove duplicate rows" to keep only one copy of any identical data row and drop the rest; the number removed is shown on screen. It's handy for de-duping a contact list or cleaning up data you exported twice. Note that even with "Add source filename column" on, the filename is not part of the duplicate check — identical content from different files still counts as a duplicate.
Are the CSV files I merge uploaded to a server?
No. The files are read into your browser only; detecting the encoding, merging, and writing all run on your device in JavaScript. Nothing is uploaded, stored, or transmitted, so it's safe for customer lists, sales data, or workplaces that forbid uploading files externally.
Can I tell which file each row came from?
Yes. Turn on "Add source filename column" and the merged output gets an extra column at the end recording the source file for each row. It's useful when you've combined CSVs from multiple branches, periods, or people and need to trace a row back to its origin.
The merged file is garbled in Excel. What should I do?
Set "Save as" to "UTF-8 with BOM (Excel)" (the default). The BOM (a marker at the start) tells Excel the file is UTF-8 so non-ASCII text displays correctly. Input files that are Shift_JIS are auto-detected and read correctly. If you only need to fix an already-garbled CSV, see csv-encoding.