CSV Cleaner and Deduplicator
Trim, deduplicate and tidy a CSV in your browser, see what changed, then download the clean file.
- Runs in your browser, files never leave your device
- Free, open source, no account, no ads
- Works offline after the first visit
Clean and deduplicate a CSV file
Drop a CSV here or choose a file
CSV, TSV or TXT. Your list is read on this device and never uploaded.
Cleaned file
Before and after
Removed rows (0)
How it works
- Open your CSV. Drop the file on the page or pick it. It is parsed on your device and you get a summary: rows, columns, duplicates, empty rows and cells with stray spaces.
- Pick the cleaning steps. Trimming and empty-row removal are on by default. Turn on deduplication and tick key columns such as email, with or without letter case.
- Check, then download. Changed cells are highlighted and every removed row is listed with its reason. Save the cleaned file and, if you want, the removed rows for review.
Questions, answered
Are my files uploaded anywhere?
No. CSV Cleaner and Deduplicator runs entirely in your browser. Your contact list or export is read into memory on your device, cleaned with JavaScript in a background worker, and never sent to a server. You can disconnect from the internet and it keeps working.
How do I remove duplicates by one column, like email?
Turn on "Remove duplicate rows" and tick the email column. Rows with the same email are treated as duplicates even when other columns differ. Tick "Ignore letter case" so Ada@Example.test and ada@example.test match. You choose whether the first or last occurrence is kept, and rows with an empty email are always kept.
Will it change my numbers, dates, leading zeros or formulas?
No. Every cell is kept as text, so postcodes like 0042 keep their zeros and dates are not reformatted. Cells that start with an equals sign are never altered. Row order is preserved, and line breaks inside quoted cells stay intact.
Is it really free?
Yes. It is open source under the MIT license, with no account, no row limits and no ads. Very large files are limited only by your device's memory. If it saves you a paid subscription, you can say thanks on Ko-fi.
Does it work offline?
Yes. After your first visit the page is cached by a service worker, so it loads without a connection. You can also install it from your browser's menu as an app.
Was this written by AI?
Yes. CSV Cleaner and Deduplicator was generated by Claude Code from a written specification inside an automated pipeline, with a test suite that runs in a real browser. The full source is on GitHub, so you can read every line before you trust it with your files.
Built by one person, given away for free
CSV Cleaner and Deduplicator is a free alternative to paid tools like Datablist CSV Cleaner and Mr. Data Converter style online CSV dedupe tools. If it earns a place in your bookmarks, a coffee keeps the updates coming.
☕ Support Or on Ko-fi