Duplicate Line Remover
Remove duplicate lines from text with case-insensitive matching and keep-first/last options.
About This Tool
The Duplicate Line Remover scans lines of text and removes any line that has already appeared earlier in the input, producing a set of unique lines. You can choose to keep the first or lastoccurrence of each duplicate. Case-insensitive mode treats "Apple", "apple", and "APPLE" as identical. Optional whitespace trimming normalizes lines before comparison.
The tool shows a summary of total lines, unique lines, and the count of duplicates removed. All processing is local β nothing is sent to a server.
How to Use
- Paste lines of text or click Sample to load an example.
- Choose whether to keep the First or Last occurrence of duplicates.
- Toggle Case-sensitive matching if you need exact case comparison.
- Click Remove Duplicates and copy the result.
Use Cases
Developers deduplicate lists of IDs, emails, or domain names exported from a database. Data analysts clean up survey responses or exported CSV columns by removing repeated entries. DevOps engineers remove repeated log entries or unique hostnames from inventory files. Writers clean up word lists or glossary terms that appear multiple times in a document. System administrators deduplicate firewall rule lists or DNS zone records.
FAQ
- Does order matter? β In "keep first" mode, the output preserves the original order, keeping the first occurrence of each line. In "keep last" mode, it keeps the last occurrence.
- What counts as a duplicate? β By default (case-insensitive, trim enabled), two lines are duplicates if their trimmed, lowercased content is identical. Enable case-sensitive mode to require exact match including capitalization.
- Is there a size limit? β No. Large inputs with thousands of lines are handled efficiently using a hash set lookup (O(n) time complexity).
- Does this work with Unicode and non-Latin text? β Yes. JavaScript strings are Unicode-aware, so deduplication works correctly with any language.