Load or paste two or more CSVs, choose union or intersection of columns and whether to add a source column, then preview the merged table and download it.
Choose union to keep every column that appears in any file, filling missing values with blanks, or intersection to keep only the columns that all files share. Union is safer when you do not want to lose data; intersection gives a tidy rectangular result.
No. When matching by header name the tool maps each file's columns onto the merged header by name, so a file whose columns are in a different order still lands in the right places. Positional stacking is available too if your files have no headers.
Yes. Turn on the source column and every merged row gets an extra field naming the file or block it came from, which makes it easy to trace a record back or to filter one source out later.