CSV Merge and Join
Join two CSV tables locally by matching key columns with left, inner, right, and full join options.
Paste two CSV tables or choose local files, then join rows where selected key columns match. Use it to enrich exports, compare lookup tables, prepare import files, or combine small browser-friendly datasets without uploading the source data.
Selecting a file replaces the left pasted input. Files are read by this page on your device only.
Selecting a file replaces the right pasted input. Files are read by this page on your device only.
Use comma-separated header names or 1-based column numbers.
Enter the same number of key columns as the left table.
How to use
Put the primary table in the left input and the lookup or enrichment table in the right input. Choose the delimiter, confirm whether both files have header rows, then enter matching key columns. Key columns can be header names such as customer_id and id, or 1-based column numbers such as 2 and 1.
Left joins keep every left row and fill unmatched right-side fields with blanks. Inner joins keep only matched rows. Right joins also include unmatched rows from the right table, and full outer joins keep unmatched rows from both sides. If a key appears multiple times on the right, each matching pair is emitted so one-to-many lookups remain visible.
The output is normalized CSV using the selected delimiter and line ending. Matching is text-based and does not evaluate spreadsheet formulas, infer relationships, or validate business rules. Very large joins can create many rows, so the row limit stops accidental browser tab overload. Private data should only be opened on devices and pages you trust.
