CSV Merge — Combine CSV Files Online
Merge multiple CSV files in your browser: append rows with columns matched by header, or join files on a key column with inner or left join.
🔒 Runs entirely in your browser — nothing is uploadedTwo ways to combine CSV files
Data rarely arrives in one piece. Monthly exports, regional reports and separate systems each produce
their own CSV file, and sooner or later you need them in a single table. CSV Merge
offers the two operations people need most. Append rows stacks files on top of each other,
which is ideal for combining January, February and March exports into one year-to-date file.
Join on a key column places matching records side by side, for example adding customer names
from one file to order lines from another using a shared customer_id.
When appending, columns are matched by header name rather than by position, so files with columns in
a different order, or with extra and missing fields, still line up correctly. The merged header is the
union of all headers, and cells that a file does not provide are left empty. Enable the
source_file option to add a column recording which file every row came from.
How the join works
Joins run from the first file in the list to the last. The key selector only offers columns that exist
in every file. An inner join keeps rows whose key is found in all files, while a left
join keeps every row of the first file and leaves the extra columns blank when no match exists.
If a key appears several times in a later file, one output row is produced for each match, exactly
like a SQL join. Keys are compared after trimming surrounding spaces, and empty keys are never matched.
Columns whose names clash with earlier ones receive a numeric suffix such as name_2.
Private and dependable
Each file's delimiter is detected automatically, quoted fields with commas or line breaks are handled, and a UTF-8 byte-order mark at the start of a file is ignored. Everything runs locally in your browser; the files are never uploaded, which keeps customer lists and financial exports on your device. Review the preview of the first 100 rows, then download the complete merged file with a comma, semicolon, tab or pipe delimiter. For more complex combinations, such as filters or aggregations across files, try the SQL on CSV tool.
How to use
- Add CSV filesDrop two or more CSV files. Use the arrows to set their order; the first file is the base table.
- Choose a merge modeAppend rows to stack files, or join them on a key column that exists in every file.
- Merge and previewClick Merge files and check the combined table preview.
- DownloadSave the merged CSV with your preferred delimiter.