Diff Checker FREE

No. The comparison runs in this tab, in JavaScript, on the text in the two boxes. There is no upload and no request: the page has no API call to make, nothing is written to storage, and closing the tab leaves nothing behind. That is worth being specific about, because a diff tool is where people paste contracts, credentials in config files and code they do not own.

Green is a line that exists only in the second text, red a line that exists only in the first, and a red-and-green pair is one line that was rewritten - the words that actually moved are marked inside it. The state is carried by the background, by the line numbers and by the plus and minus signs together, not by colour alone, so the result is still readable if you do not distinguish red from green.

Ignore case matches lines that differ only in capitals. Ignore whitespace collapses runs of spaces and tabs and trims the ends, so an indentation change stops being a difference - it does not delete spaces entirely, so "ab" and "a b" are still different lines. Ignore blank lines drops empty lines from the comparison while the line numbers still count them, so a number here is the number in your file. Lines always print exactly as you typed them; the options change what counts as a match, not what is shown.

Text files, up to 2 MB each: .txt, .md, .csv, .json, .xml, .yml, .html, .css, source files, logs, subtitles. You can drop a file onto either box. A PDF, a .docx or a spreadsheet is not text, so it is refused by name rather than shown as a screen of binary - convert it first, or use the File Converter.

It is the format `patch`, `git apply` and every code review tool reads: a header naming the two sides, then hunks marked with the line ranges they cover and the lines themselves prefixed with a space, a minus or a plus. Copy it into a review, attach it to a ticket, or save it as a .diff file and apply it with `patch -p0 < file.diff`.

Ten thousand lines with a change in the middle is instant: the comparison trims what matches at the ends first, then works from the lines that appear exactly once on each side, which is also what makes a block that was moved read as a move rather than as a deletion and an addition. The result is painted in slices of 600 lines with a button for the rest, because a browser laying out ten thousand rows of monospaced text at once is a browser that stops responding. If two very large texts have nothing in common at all, the tool says so and reports the change coarsely instead of grinding through it.