Safe Column Merge
Safely add columns from one CSV to another
Load your base CSV file and the CSV file you want to copy columns from. Row counts are compared, then a chosen identifier column is checked row by row, before anything is copied — so columns are never appended if the rows might not actually line up.
- Load the base CSV file (A) — the file the result is built from.
- Load the source CSV file (B) — the file you want to copy columns from.
- Row counts are compared automatically.
- Choose the identifier column in each file and check they correspond row by row.
- Choose which columns from B to add, then download the safely merged result.
File A — base file
File B — source of columns
Both CSV files are processed locally in your browser and are not sent to the server. Only anonymous usage events are sent — never file names, file contents, column names or row values. No fingerprinting is used.
Row counts
- File A rows
- —
- File B rows
- —
Check that rows correspond
Choose columns to add from B
What this tool does
- What to choose
- Two CSV files with a header row: file A (the base file) and file B (the file to copy columns from).
- What is checked
- Row counts are compared, then a chosen identifier column is compared row by row before anything is copied.
- What you get
- File A with the selected columns from B appended, in the same row order, only after both checks pass.
- Where the files go
- Nowhere. Loading, checking and merging happen in your browser, and file contents are never sent to the server.
What this tool does not do
- It does not join files by a key or reorder rows — rows are compared strictly by position.
- It does not fuzzy-match identifiers, reconcile schemas, or auto-fix mismatches.
- It does not repair encodings or infer column types — it is not a general CSV cleaner.
- It never overwrites an existing column in A with a same-named column from B without telling you.