Text Diff Checker

Paste both versions here. For Word documents, use Review then Compare, which understands formatting changes as well as text.

No. The comparison runs in JavaScript on this page, which matters when the two versions are contract drafts or config files.

It finds the longest sequence of lines common to both texts and treats everything else as an insertion or deletion. That is why inserting one line at the top does not mark the whole file as changed.

This one works on lines, which is the right granularity for code, config and structured text. For prose where you want word-level detail, paste one sentence per line first.

diff -u old new for a unified diff, or git diff --no-index old new to get git's colouring and formatting on files outside a repository.

Almost always trailing whitespace or line endings - a file saved on Windows uses CRLF and one saved on macOS uses LF. Both are invisible and both count.

Comfortably a few thousand lines. The comparison is quadratic in the number of lines, so very large files will slow the page down.

Yes, but format both sides first so keys line up on their own lines. Comparing minified JSON produces one enormous changed line.