List & CSV Deduplicator
Remove duplicate entries from lists and CSV files by column — order-preserving, entirely in your browser
Examples
Keyword list cleanup
apple\nbanana\napple\n cherry\nCherry3 unique: apple, banana, cherry · removed: apple ×1, cherry ×1With trim + case-insensitive on; first-seen casing wins the output.
Customer CSV by email
5,000 rows, key column: emaile.g. 5,000 → 4,812 unique · 188 droppedFirst row per email survives with all other columns intact; quoting round-trips.
About this tool
Two deduplication modes share one contract: keep the first occurrence, preserve original order, and report everything removed. Plain-list mode compares lines with optional trimming and case folding; CSV mode parses with full RFC 4180 quoting and dedupes by any column you choose.
Everything runs on a Set of normalized keys — linear time, comfortable with hundreds of thousands of rows — and nothing leaves the browser.
How to use
Paste your data
Plain list (one entry per line) or CSV with a header row.
Choose options
Trim, case-insensitive comparison, empty-line skipping; in CSV mode pick the key column.
Review the report
Summary counts plus a removed-duplicates list with repeat counts.
Export
Copy the clean output or download as .txt / .csv.
Use cases
Exported contacts
Collapse repeated email addresses while keeping the earliest row per contact.
ID list hygiene
Clean pasted user IDs or keywords from multiple log excerpts.
Modes
| Mode | Deduplicates by |
|---|---|
| Plain list | Whole line (with optional trim / case folding / empty skip) |
| CSV | Any single column you pick, with full quoting support |
Common mistakes
Mistake:Deduping CSV on the whole row
Fix:Pick the key column — rows often differ in timestamps while being the same record.
Mistake:Expecting 'keep newest' behaviour
Fix:First occurrence wins by design; sort by date before pasting to keep the newest.
Frequently asked questions
Related guides
References & standards
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