Question 1

What does the CSV File Joiner do?

Accepted Answer

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.

Question 2

What is the difference between append and join mode?

Accepted Answer

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.

Question 3

How are duplicate headers handled?

Accepted Answer

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.

Question 4

What extra features does this tool have?

Accepted Answer

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).

Question 5

Are my CSV files uploaded anywhere?

Accepted Answer

No. All parsing and merging happens in your browser using pure JavaScript. Your data never leaves your device.

Question 6

What's the maximum CSV size?

Accepted Answer

There's no hard limit, but very large files (> 100MB) may slow the browser. We use efficient array operations and show progress for merges.

CSV File Joiner

How to use