Case-Insensitive Deduplicator

Simply paste your text into the input area or upload a .txt/.csv file. Toggle the Ignore Case option ON (default), then click Deduplicate. The tool normalizes every line to lowercase for comparison while preserving the original capitalization of the first occurrence. For example, 'John Doe', 'john doe', and 'JOHN DOE' are all treated as duplicates — only the first version ('John Doe') appears in the output.

No. Every deduplication is performed entirely in your browser using native JavaScript Set and String operations. Your data is never sent to any server, stored in any database, transmitted over any network, or logged anywhere. The tool works fully offline after the initial page load. All processing is 100% local.

Yes, by default. The tool preserves the original capitalization of the first occurrence of each unique line. For example, if 'John Doe' appears first, followed by 'john doe' and 'JOHN DOE', the output will contain 'John Doe'. You can also use the Output Case dropdown to convert all output to lowercase, UPPERCASE, or Title Case if needed.

Case-insensitive deduplication means 'Apple', 'apple', 'APPLE', and 'ApPlE' are all treated as the same entry. Standard deduplication treats these as different because it compares strings literally — 'Apple' !== 'apple'. Case-insensitive deduplication normalizes each line to lowercase before comparison, so capitalization differences are ignored while the original text of the first occurrence is preserved.

Yes. The O(N) Set-based algorithm processes 100,000 lines in milliseconds. For datasets exceeding 25,000 lines, processing automatically switches to a dedicated Web Worker, keeping the browser fully responsive. You can scroll, type, switch themes, and copy results while large datasets are processed in the background. The tool handles 500,000+ lines smoothly.

The tool clones the input array to avoid mutating the original data. It then creates a normalized comparison array using .toLowerCase() combined with optional .trim(). Normalized values are stored in a native JavaScript Set for O(1) lookups. When a normalized value already exists in the Set, the line is removed as a duplicate. When it does not exist, the normalized value is stored in the Set and the original line is added to the output — preserving the original capitalization of the first occurrence. All processing runs in O(N) time.

Yes. Toggle Trim Whitespace ON (default) to strip leading and trailing whitespace from each line before comparison. This ensures that 'John' and ' John ' and 'John ' are all treated as duplicates. Trimming happens before the case-insensitive comparison, so both normalization steps work together for maximum deduplication accuracy.

Yes. Toggle Remove Blank Lines ON (default) to strip empty lines before deduplication. This ensures blank lines are not counted in the statistics or included in the output. Blank lines are removed before deduplication processing.

Yes. After deduplication, you can copy the results to clipboard, download as a .txt file, or download as a .csv file. The CSV format handles special characters and delimiters correctly. All export actions are instant and happen entirely in your browser with no data transmission.

Yes. Use the Sort Output dropdown to reorder results after deduplication. Options include None (preserve original order), A-Z, Z-A, and By Length. Sorting is applied after deduplication and does not affect the deduplication algorithm itself.

The tool supports .txt and .csv file uploads via the File Upload button, drag-and-drop, or copy-paste. Files are read using the FileReader API and never leave your browser. After parsing, the tool displays the total line count to confirm successful loading.

The statistics panel shows Original Lines (total input count), Duplicates Removed (number of case-insensitive duplicates found), Unique Lines (lines in the deduplicated output), and Completed In (processing time in milliseconds). Statistics update live after each deduplication.