Duplicate Line Remover

Three strategies sound alike and return different lists. Keep First holds the earliest copy of each line, Keep Last holds the latest, and Remove All discards every line that appeared more than once, leaving only the entries that were already unique. The Duplicate Line Remover puts all three on tabs so you can watch the count move between them.

The built-in sample makes that concrete: 8 fruit names in which apple, banana and cherry each appear twice. Keep First returns 5 lines opening on apple. Keep Last also returns 5, in the different order apple banana date cherry elderberry, because it walks the list backwards. Remove All returns just 2, date and elderberry.

Three checkboxes sit above the panes. Trim lines is on by default, since trailing whitespace is the usual reason a real duplicate slips through. Case-sensitive is off, so Apple and apple collapse together. A sort control on the right can order the survivors afterwards. None of it leaves the page.

Running a Dedupe Over a Pasted List

1. The box opens on an 8-line fruit list; Sample swaps in a different duplicate-heavy list each press, and you can paste your own one item per line.
2. Pick a tab. The Output label updates live to read (5 kept · 3 removed), so strategies can be compared without copying anything.
3. Set the checkboxes. Switching Case-sensitive on generally raises the kept count, because lines that differed only in capitalisation stop matching each other.
4. Choose a Sort of A→Z or Z→A when the surviving order does not matter, or leave None to preserve it.
5. Read the three cards along the bottom for Total Input, Unique Kept and Duplicates Removed, then hit Copy and watch for the Copied! 🚀 badge.

What Happens When Lines Differ Only in Case

• With Case-sensitive off the comparison key is lowercased, but the output keeps the spelling of whichever line won. Under Keep First, iPhone ahead of IPHONE preserves iPhone.
• Keep Last inverts that, so the final spelling in the file is the one that survives.
• Trim lines rewrites each line before comparing, which means the copied output has lost its indentation. Switch it off before deduplicating code.
• Leave Ignore empty off and blank lines are ordinary values, so Keep First collapses every blank line in the file into one and quietly reflows a double-spaced document.
• Remove All can return nothing whatsoever. Feed it a list in which every entry appears twice and the pane sits empty with (0 kept · 8 removed) beside it.