Duplicate Line Remover
Free online tool to automatically detect and remove duplicate lines from text files, code, and data lists. Real-time preview with statistics, clipboard copy, and file download features.
Duplicate Line Remover
All processing is done in your browser. Your data is never sent to a server. Only the first occurrence of each line is kept, and all subsequent duplicates are removed.
What is Duplicate Line Remover?
Duplicate Line Remover is a free online tool that automatically detects and removes duplicate lines from text files, code, or data lists. Simply enter text or upload a file, and it will detect duplicate lines in real-time, keeping only the first occurrence and removing all others.
It supports case-sensitive options and provides statistics including original line count, result line count, removed line count, and removal percentage. The processed result can be copied to clipboard or downloaded as a TXT file, and all processing is done in your browser to ensure data security.
When to Use This Tool
- Data Cleaning – Remove duplicate records from CSV files, logs, or database dumps
- Code Cleanup – Remove duplicate dependencies from import or require statements
- URL Lists – Remove duplicate URLs from web crawling results or bookmark collections
- Email Lists – Remove duplicate emails from subscriber lists or contact databases
- Keyword Organization – Remove duplicate items from SEO keywords, tags, or category lists
- Configuration Files – Remove duplicates from hosts files, .gitignore, or environment variable files
Key Features
- Real-time Preview – Duplicate lines are removed instantly as you type, and results are displayed immediately.
- Case Sensitivity Option – Choose whether to distinguish between uppercase and lowercase letters.
- Statistics Display – Shows original line count, result line count, removed line count, and removal percentage in card format.
- File Upload – Upload TXT files to easily process large amounts of text.
- One-Click Copy – Copy the processed result to clipboard with a single click.
- File Download – Download the result as a TXT file for immediate use.
- Client-Side Processing – All processing is done in your browser, so data is never sent to a server.
How to Use
- Enter Text – Paste or type text directly into the input field on the left.
- Upload File (Optional) – Click the ‘Upload File’ button to load a TXT file.
- Set Options – Check the ‘Case Sensitive’ checkbox to distinguish between uppercase and lowercase.
- View Results – The deduplicated result and statistics are automatically displayed on the right.
- Use Results – Use the ‘Copy’ button to copy to clipboard or the ‘Download’ button to save as a file.
How Duplicate Detection Works
Duplicate Line Remover uses JavaScript’s Set data structure for high-performance duplicate detection. It reads each line sequentially, includes the first occurrence in the result, and ignores subsequent identical lines.
Case Insensitive Option: When checked, “Apple” and “apple” are considered the same line. When unchecked, they are treated as separate lines.
Order Preservation: The original order of lines is maintained after duplicate removal. Lines are ordered by their first occurrence, and are not re-sorted alphabetically or by any other criteria.
Blank Line Handling: Blank lines are also considered as lines. If there are multiple blank lines, only the first one is kept and the rest are removed.
Frequently Asked Questions
Is there a limit to the text size that can be processed?
Large files can be processed within browser memory limits. Typically, it works smoothly with hundreds of thousands of lines, and since all processing is done on the client side, there are no server capacity restrictions.
Does duplicate detection consider spaces and special characters?
Yes, spaces, tabs, and special characters are all considered. “apple” and “apple ” (with trailing space) are recognized as different lines, and spaces are still distinguished even when case sensitivity is disabled.
Does the result change the order from the original?
No, the original order is maintained. Duplicate lines are removed, but the remaining lines are arranged in the order they first appeared in the original.
Is the entered data sent to a server?
No, all processing is done within your browser and data is never sent to a server. You can safely process personal or sensitive data.
Can encoding issues occur when uploading files?
TXT files are read in UTF-8 encoding. Most modern text files are processed without issues, but if characters appear garbled, try saving the file as UTF-8 before uploading.
Can CSV or code files be processed?
Only TXT files can be directly uploaded, but you can copy and paste the contents of CSV or code files into the input field for processing. Since duplicates are removed line by line, text in any format is supported.
How are blank lines handled?
Blank lines are also considered as lines. If there are multiple blank lines, only the first blank line is kept and the rest are removed. To completely remove blank lines, we recommend post-processing the result with another text tool.