Remove Lines Containing/Not Containing tool provides a user-friendly interface for manipulating text files or pasted text by filtering and removing lines based on user-defined criteria. It features options to upload a text file or directly paste text, specify a filter string, and choose whether to remove lines containing or not containing the filter. Upon applying the filter, the tool displays the modified text in a textarea and highlights the original text with matched lines. Users can copy the result to the clipboard or download it as a text file. Error messages are displayed for empty inputs or when there’s no result to download, enhancing usability. Overall, it’s a versatile tool for text processing tasks.