CSV Merger
Drop multiple CSV files to merge them together. Stack rows, join on a key column, or concatenate all columns.
Drop 2 or more CSV/TSV files here, or click to select.
.csv, .tsv, .tab · Max 500 MB
Drop multiple CSVs
Drag two or more CSV files onto the dropzone. They're parsed in your browser.
Pick a merge mode
Stack appends rows (requires identical headers). Join performs SQL-style INNER, LEFT, or RIGHT joins on a key column you pick. Concat takes the union of all columns and null-fills.
Configure the merge
For Join, pick the key column. For Stack and Concat, no extra setup is needed.
Download the merged CSV
Preview the merged table, then click Download to save the result.
- Does this tool upload my files?
- No. Every parse, transform, and download runs entirely in your browser using JavaScript and Web Workers. The file never leaves your device — there is no upload endpoint and no server-side processing.
- What happens to duplicate keys in a Join?
- Duplicate keys produce a Cartesian product — every left match is paired with every right match. Use CSV Dedupe first if you want one row per key.
- Can I merge more than two files with Join?
- Join works on exactly two files. For more, run merges in pairs: join A and B into AB, then join AB with C.
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