CSV File Joiner
Merge multiple CSV files into one with header-aware alignment, column matching, dedup, and export. Supports inner/outer join modes, custom delimiters, column reorder, row sorting, filtering, and preview. 100% client-side.
About CSV File Joiner
Merge multiple CSV files into one with header-aware alignment, column matching, dedup, and export. Supports inner/outer join modes, custom delimiters, column reorder, row sorting, filtering, and preview. 100% client-side. Everything runs locally in your browser — your data never leaves your device.
How to use
- Enter your input in the tool above.
- Adjust any options to your preference.
- Use the Copy or Download buttons to save the result.
- Everything happens locally — your data never leaves your browser.
FAQ
What does the CSV File Joiner do?
It merges multiple CSV files into one. Headers are aligned automatically — files with different column orders or extra/missing columns are joined correctly using column-name matching. You can append (stack rows) or join (inner/outer) by a key column.
What is the difference between append and join mode?
Append mode stacks all rows from all files under a unified header (union of all columns; missing cells become empty). Join mode merges files side-by-side using a shared key column — inner join keeps only matching rows, outer join keeps all rows from every file.
How are duplicate headers handled?
When appending, only the first file's header row is kept; subsequent files' header rows are automatically skipped so they don't appear as data. You can toggle this off if your files have no headers.
What extra features does this tool have?
10 extras: (1) Drag-drop multiple files. (2) Column reorder (drag columns to reorder before export). (3) Dedup rows (by full row or by key column). (4) Sort by any column (asc/desc, numeric-aware). (5) Filter rows by column value / substring. (6) Per-file stats (row count, column count, size). (7) Preview first N rows of merged output. (8) Custom delimiter (comma, tab, semicolon, pipe, custom char). (9) Encoding detection (basic BOM sniffing). (10) History (localStorage — last 10 merge configs).
Are my CSV files uploaded anywhere?
No. All parsing and merging happens in your browser using pure JavaScript. Your data never leaves your device.
What's the maximum CSV size?
There's no hard limit, but very large files (> 100MB) may slow the browser. We use efficient array operations and show progress for merges.
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