THE FEUTEX TOOLKIT

CSV Duplicate Checker

Find duplicate rows or duplicate keys in a CSV. Choose columns, delimiter, header, and output unique or duplicate-only CSV — runs client-side.

Delimiter

Auto picks the delimiter from the first non-empty line.

Custom delimiter

Used only when Delimiter = Custom.

Key columns (optional)

If Compare full row is off, duplicates are detected by these columns (names require header).

When making unique CSV

Output mode

Show top duplicates

0 = don’t list keys (counts still shown).

CSV input

Tip: For column-based matching, uncheck Compare full row and enter key columns.

Output

Privacy: runs locally in your browser. No uploads, no tracking scripts.

How to use

Use this tool to detect duplicates by full row or by selected key columns.

Paste your CSV into the input box.
Pick a delimiter (or keep Auto), and set whether the first row is a header.
Choose Compare full row or enter key columns (names or 1-based indexes like 1,3).
Click Check duplicates.
Switch Output mode to get a unique CSV or a duplicate-only CSV.

Does this CSV duplicate checker upload my file?

No. It runs client-side in your browser; the CSV stays on your device.

Can I detect duplicates by a specific column (like email)?

Yes—turn off Compare full row and enter key columns by name (with header) or by 1-based index (e.g. 1,3).

What counts as a duplicate row?

Rows are duplicates when their comparison key matches (full row or selected columns), after applying trim/case options.

Does it handle quoted CSV fields and commas inside quotes?

Yes. Quoted fields and escaped quotes ("") are parsed correctly.

How do I remove duplicates and keep only unique rows?

Set Output mode to Unique CSV (or Report + Unique CSV) and choose whether to keep the first or last occurrence.

How do I export only the duplicates?

Use Duplicate-only CSV output and choose whether to include the first occurrence in the duplicate export.

Why does Auto delimiter pick the wrong separator?

Auto uses the first non-empty line; if your header is unusual, set the delimiter explicitly (comma/tab/semicolon/pipe/custom).

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