CSV Merge & Dedupe

Paste two CSV tables or open the files, pick the key column of each, and get one merged table without duplicates. Everything stays in your browser.

Your data is read and merged by your browser. Nothing is uploaded, saved or sent anywhere.

Table A (CSV, first row = headers)

Open file

Delimiter

Comma · 3 columns · 3 data rows

Table B (CSV, first row = headers)

Open file

Delimiter

Comma · 3 columns · 3 data rows

Key columns (rows with the same key are duplicates)Key in Table AKey in Table B

Column mapping: which column of Table B feeds each column of Table A

Email← email (key)

Name ←City ←

Add the columns that only exist in Table B

Keep

Ignore case (Ann = ann)Trim spaces around keysFill empty cells from the removed copy

Conflicts (1)

Conflicts between duplicate rows
Key	Column	Values found	Kept
ann@example.com	Name	Ann Lee \| Ann Leigh	Ann Lee

Merged table preview
Email	Name	City	phone
ann@example.com	Ann Lee	Paris	555-0102
bob@example.com	Bob Ray		555-0101
cy@example.com	Cy Moon	Rome
dee@example.com	Dee Park		555-0103

Paste CSV into Table A and Table B, or press “Open file” to read a file from your device. The delimiter is detected for you.
Choose the key column of each table (an email, an ID, a SKU) and check how the other columns line up.
Pick which copy to keep for duplicate keys, and whether to ignore case or fill empty cells from the removed copy.
Review the conflicts, then copy or download the merged CSV.

Mailing and contact lists
Combine a newsletter export with a customer list and keep each email address only once.
Product and inventory sheets
Merge two supplier catalogs by SKU and see where the prices or names disagree.
Survey and event sign-ups
Join registrations from two forms without counting the same person twice.

How are duplicates found?: Rows are compared on the key column only. With “Ignore case” and “Trim spaces” on, “Ann@Mail.com ” and “ann@mail.com” count as the same key. Rows with an empty key are never removed. By default the first copy is kept; choose “Last” to keep the most recent one.
What is a conflict?: When duplicate rows have different non-empty values in the same column, that is listed as a conflict, with the value that was kept. “Fill empty cells” is on by default: an empty cell in the kept row is completed with the value from a removed copy, so no data is lost; non-empty cells are never overwritten. Turn it off to keep the kept row exactly as it was.
Which CSV files are supported, and is there a size limit?: Commas, semicolons and tabs are detected automatically, quoted cells (including doubled quotes and line breaks inside a cell) and a UTF-8 byte order mark are handled. Each table is limited to 5,000 data rows and files to 5 MB, and a message tells you when the limit is hit. Nothing is uploaded: the files are read by your browser.