What it does
Loads a CSV file from your device. The file stays in the browser: nothing is uploaded.
Treats rows as duplicates when every selected column matches. All columns are selected at first, which removes identical rows only.
Applies three rules before comparing: ignore capitalisation and ignore extra spaces at the start and end of a value (both on), and ignore punctuation (off, because it matters in fields such as product codes).
Keeps the first or the last match, and exports both halves: the clean list and the removed rows.
Why it is useful in class
Duplicates are rarely identical. "Anna.Berger@Northwind.example " and "anna.berger@northwind.example" are the same address, but a plain comparison says otherwise. The tool makes the rules visible as switches, so learners can see how each one changes the result instead of trusting a black box.
Ideas for class
Work through the contact list worksheet: one messy file, five questions, solutions included.
Discuss what a "record" is: one person, one email address or one company? Each answer needs a different key column.
Connect it to data protection: keeping one clean record per person is part of data accuracy under GDPR Article 5.
Using this page
The tool is free to use. This description and the ideas on it are licensed under CC BY 4.0.