CSV Merger
Drop multiple CSV files to merge them together. Stack rows, join on a key column, or concatenate all columns. Your data never leaves your browser.
Drop 2 or more CSV/TSV files here, or click to select.
CSV, TSV · Max 2 GB
How to use CSV Merger
- 1
Drop multiple CSVs
Drag two or more CSV files onto the dropzone. They're parsed in your browser.
- 2
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.
- 3
Configure the merge
For Join, pick the key column. For Stack and Concat, no extra setup is needed.
- 4
Download the merged CSV
Preview the merged table, then click Download to save the result.
Frequently asked questions
- 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 Deduplicator 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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