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Tools / CSV Merger

CSV Merger

Drop multiple CSV files to merge them together. Stack rows, join on a key column, or concatenate all columns.

Runs entirely in your browser

Drop 2 or more CSV/TSV files here, or click to select.

.csv, .tsv, .tab · Max 500 MB

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 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.
CSV Dedupe

Remove duplicate rows from a CSV. Pick which columns to compare and what to keep.

CSV Filter & Transform

Build a visual filter pipeline with AND/OR logic, pick columns, sort, and export.

CSV Viewer

View and explore CSV files with sorting, filtering, and column type detection. Handles 100k+ rows.