Explicit headers · Predictable output
Merge CSV files
Combine two or more CSV files. Require an exact header match or deliberately create an ordered union.
Merge CSV files locally
Choose two or more files, up to 50 MB combined. Nothing is uploaded.
Append rows from each file in order. This does not join records by an ID.
- Choose CSV files
Select two or more files, up to 50 MB combined, or try the samples.
- Check headers and order
Use Strict match or Header union; arrange the files in the row order you need.
- Download merged CSV
Check the merged preview, then save one CSV with its header and appended rows.
Predictable by default
No silent column shifts
Strict mode prevents a value from sliding under the wrong column just because one file changed header order. Union mode is available when files intentionally contain different columns.
Union mode requires unique, nonblank headers in every file. That makes the mapping explicit instead of guessing which duplicate or blank column a value belongs to.
Plain answers
CSV merge questions
What is strict header matching?+
Every file must have exactly the same source headers in the same order. A mismatch names the file that needs attention and blocks the download.
How does header union work?+
Union mode keeps headers in first-seen order, maps cells by exact header text, and leaves a cell empty when a file does not contain that header.
How does merging work?+
Choose two or more CSV files, require matching headers or select an ordered header union, then download the combined CSV.