Compare two texts line by line and see additions and removals highlighted, with options to ignore trailing whitespace and letter case. Free, in your browser.
How the diff checker works
The two texts are split into lines and compared with the same longest-common-subsequence approach used by version-control diffs: the algorithm finds the largest set of lines the texts share in order, and everything outside that set is marked as removed (from the original) or added (in the changed text). Unchanged runs at the start and end are skipped up front, so even large documents with a small edit compare instantly. The options normalize each line before comparison — trailing spaces or letter case differences can be ignored — while the display always shows your original text.
LCS(a, b) → longest common subsequence of lines; rest is + / −Frequently asked questions
Are my texts uploaded anywhere?
No. The comparison runs entirely in your browser. Neither text is sent to a server, logged or stored, and the texts never appear in the page URL — only the two ignore options do.
Why does it compare lines instead of words or characters?
Line-level diffs are what code review and version control use: they stay readable on big inputs and make moved or edited blocks obvious. A word-level diff of two long documents tends to dissolve into noise. Paste prose one sentence per line if you want finer-grained comparison.
Is there a size limit?
Comparison cost grows with the product of the two line counts that actually differ. Identical leading and trailing lines are skipped first, so realistic edits to large files are fast. Only when both texts differ across many thousands of lines will the tool refuse and ask you to compare smaller sections.
Last updated: 8 July 2026
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