Diff Checker
Compare two blocks of text side by side and instantly see additions, deletions, and unchanged lines.
Frequently Asked Questions
What algorithm does this diff checker use?
It uses a Longest Common Subsequence (LCS) based diff algorithm. LCS finds the longest sequence of lines common to both texts, then marks remaining lines as additions or deletions — the same core approach used by Git and Unix diff.
Can I compare large files?
Yes. The tool runs entirely in your browser, so there are no upload limits. However, very large files (tens of thousands of lines) may take a moment to compute because the LCS algorithm has O(n×m) time complexity.
Is my data sent to a server?
No. All processing happens locally in your browser. Your text never leaves your machine, making it safe for comparing sensitive code, configs, or credentials.
What counts as a 'changed' line?
This tool performs a line-by-line comparison. If a line exists in the original but not in the modified text, it is marked as a deletion (red). If it exists in the modified but not the original, it is an addition (green). Lines present in both are unchanged.
Does it detect moved lines?
Not directly. A moved line appears as a deletion at its old position and an addition at its new position. This is consistent with how standard line-based diff tools work.