Why does it say the comparison is too large?

The LCS table is old lines × new lines. Identical top and bottom sections are trimmed away first, but past four million cells, roughly 2,000 lines against 2,000 differing lines, the table stops fitting comfortably in memory, so the tool asks for a smaller section rather than freezing your tab.

Is trailing whitespace treated as a change?

By default yes, because the lines genuinely differ. Turning on Ignore whitespace trims each line and collapses its internal runs of spaces and tabs before matching, while the rows still display the original text, only the matching rule relaxes, not what you see.

Diff Checker

No upload · runs in your browser

Whitespace

Case

Original

0 lines

Changed

0 lines

Unified diff

Paste text into both panes to see the differences.

Both versions are compared in your browser, neither is uploaded.

How it works

Diff checker that compares two texts line by line

Paste the old version on the left and the new one on the right to get a line-by-line unified diff, with added and removed lines highlighted and counted.

What this does

A true LCS diff, so unchanged blocks stay aligned instead of drifting out of step
Old and new line numbers on every row, with @@ hunk headers between the changes
Ignore whitespace collapses runs of spaces and tabs and trims each line before matching
CRLF is normalised on both sides, so a Windows file never reports every line as changed
A +added / −removed tally beside the unchanged count, with the first 2,000 rows drawn and the whole diff downloadable

FAQ

No. The comparison is line-level, so a line with a single character altered shows up as one removal and one addition. When you need word-level detail, diff the two lines on their own.

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