Side-by-side, line-aligned diffing
This compares two code snippets line by line and shows them side by side, the way most code review tools present a diff - removed lines highlighted on the left with a matching blank space on the right, and added lines highlighted on the right with a matching blank space on the left, so both versions stay vertically aligned as you scroll through them.
How this differs from this site's Diff Checker tool
The Diff Checker tool highlights word-level changes within running text, which suits prose and sentence-level editing comparisons. This tool compares whole lines side by side instead, which better suits code, config files, or any content where line structure itself matters - a single changed character still marks the entire line as different, which is exactly the behavior most code review tools use.
Why the algorithm looks for the longest common subsequence
Rather than naively comparing line 1 to line 1, line 2 to line 2, and so on, the underlying algorithm finds the longest sequence of lines that appear unchanged in both versions, then marks everything else as added or removed around that shared backbone - this is what correctly aligns a diff even when lines have been inserted or deleted partway through, rather than mislabeling everything after an insertion as "changed."
Why this treats every line as plain text
The comparison works purely on exact line-text matching, with no understanding of code syntax, indentation semantics, or language-specific structure - which is actually what makes it work identically well for any programming language, config format, or plain text, at the cost of not offering syntax highlighting or structural awareness.