Merge CSV Files: how it works
How it works
- Open the first CSV with the button above. Then choose Add rows from another CSV and pick the second file; repeat for each further file, one at a time.
- The header rows must match exactly: same columns, same names, same order, same delimiter. If they do not, the merge is refused, the differing columns are listed, and your open file stays as it was.
- Review the report of added and total rows, check for duplicates across the files or run Doctor, then save. Save downloads the combined file as a new CSV; your original files are never overwritten.
What stays exactly the same
Rows from every file keep their original bytes: quoting, spacing and line endings are not normalized. If the files use different line endings, Doctor reports the mix instead of rewriting it.
Adding a file starts a new undo history, so an earlier edit cannot be undone afterwards; edits made before merging are included in the result. The combined file must stay within 32 MiB, the same limit as opening a file.
Limits
Files are uploaded to the cellsmith.app server and held in memory, not kept only in your browser. The web version accepts UTF-8 text files up to 32 MiB each. Files expire 30 minutes after the last activity; opening another file or restarting the server also clears the current document and unsaved work.
Questions about this tool
Can I merge CSV files with different columns?
Not yet. The header of each file must match exactly, including column order. When it does not, the tool lists which columns differ so you can fix the source file and try again.
In what order are the files combined, and how many can I add?
Rows follow the order you add the files: the open file first, then each added file, keeping each file's own row order. One file is added at a time, and the combined file must stay within 32 MiB. Files are uploaded to the cellsmith.app server, held in memory and deleted after the retention period.
How do I remove rows that appear in both files?
After merging, choose Check duplicates. It previews exact duplicate rows across the combined file, and you can remove them as one undoable step.