How the merge works
The tool stacks your files — it puts all their rows into one file, one after another. The clever part is the alignment: instead of assuming every file has its columns in the same order, it reads each file’s header and lines up the data by column name. So these three common situations all just work:
| Your files | What happens |
|---|---|
| Identical columns (the usual case) | Rows are appended under a single shared header |
| Same columns, different order | Each row is placed by name, so nothing ends up in the wrong column |
| One file has an extra column | The extra column is added to the merged header; other files’ rows are blank there |
Tick Add a source-file column and every row also records the file it came from — invaluable when you merge a folder of monthly exports and later need to trace a row back to its month.
When you’d use it
The classic case is periodic exports: twelve monthly sales files into one annual file, a batch of daily logs, or the same report pulled from several regions. Rather than opening each in Excel and copy-pasting (which risks the usual Excel damage to codes and dates), you combine them once, cleanly, in the browser and hand the single file to whatever comes next.
What it does and doesn’t do
Merging stacks rows vertically; it does not de-duplicate or join. Two honest limits worth knowing:
- Duplicates are kept. If the same row is in two files, it appears twice. Run the result through the CSV Cleaner afterwards to drop duplicate rows in one pass.
- This is a vertical stack, not a lookup. If you instead need to join two files side by side on a shared key (matching a customer list to its orders by ID), that’s a different operation — this tool adds rows, it doesn’t match columns across files.
Combined your files? Send the result through the cleaner to drop duplicate and blank rows, or the encoding checker if the pieces came from different systems.
Open the CSV cleaner →Related
Prefer Excel’s Power Query or the command line, or want the methods compared? See the guide to merging multiple CSV files. Different delimiters across your files? Normalise them first with the CSV ⇆ TSV converter. Not sure a file is UTF-8? Run the encoding checker. And every Excel-and-CSV pitfall is written up in the guides.
Frequently asked questions
How do I merge multiple CSV files into one?
Drop all the files into the tool above (or pick them together), then click Merge & Download. They’re stacked into one file in the order shown, the header is taken once, and every data row is lined up by column name. It runs in your browser, so nothing is uploaded.
What if the files have different columns or a different column order?
They still line up correctly. The merged header is the union of all the files’ column names, and each row is placed by matching its own header names — so a file with columns in a different order, or with an extra column, is aligned rather than misplaced. Columns a file doesn’t have are left blank for its rows.
Can it tell me which file each row came from?
Yes. Tick Add a source-file column and the merged file gains a column recording the original filename for every row — handy when you combine twelve monthly exports and later need to know which month a row belonged to.
Does merging remove duplicate rows?
No — merging only stacks the files, so a row present in two files appears twice. To drop the duplicates afterwards, run the merged file through the free CSV Cleaner, which removes duplicate rows in one pass.