Text Diff Checker
Find what actually changed
Word or line level diffing with whitespace and case toggles and a unified patch export.
Text Diff Checker
Runs in your browser · nothing uploaded01 — How to use Text Diff Checker
02 — Getting good results
03 — Questions
No. The diff runs entirely in this browser tab. Neither version is transmitted or stored, which matters when comparing configuration files or anything else you would not paste into a public website.
The algorithm builds a table of every line in one input against every line in the other, so memory grows with the product of the two sizes. The cap keeps a large pair of files from freezing the tab.
The same output as diff -u: a header naming both sides, a hunk header with the line counts, then each line prefixed with +, - or a space. Most review tools and mail clients render it with colour automatically.
Yes. CRLF is normalised to LF before comparing, so a file saved on Windows and the same file saved on Linux do not show as entirely different.
04 — More about Text Diff Checker
How a diff decides what changed
Comparing two texts is really the problem of finding their longest common subsequence: the longest ordered set of lines appearing in both, not necessarily adjacently. Everything in that subsequence is unchanged, and everything else is an insertion or a deletion. This produces the minimal edit script, which is why a diff highlights the one line you edited rather than declaring everything after it different. The cost is that the standard algorithm compares every line of one input against every line of the other, so time and memory grow with the product of the two lengths — the reason this tool caps input size rather than letting a large pair of files lock up the page.
Why "changed" is not a diff operation
Diff output has exactly three operations: keep, insert and delete. There is no "modify", because deciding whether a line was edited or simply replaced requires judgement the algorithm does not have. A line with one corrected typo and a line replaced wholesale are indistinguishable to it — both appear as a deletion followed by an insertion. Word-level diffing is the practical answer: by comparing words rather than whole lines, the common parts of a modified sentence land in the unchanged subsequence and only the genuinely different words are marked, which is what makes a one-word correction readable instead of showing two near-identical lines side by side.
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Same shell, same shortcuts, same promise: nothing leaves your browser.