Compare two text blocks side-by-side with character-level and line-level diff highlighting.
The left and right panes hold your two text blocks, and every difference between them is marked twice: rows where the lines differ are flagged, and within each flagged row the exact changed characters are highlighted, so an edit shows as a small, precise mark rather than a whole line. The comparison is byte-for-byte. Trailing spaces, tabs, and CRLF versus LF line endings all count as real changes, which is the surprise most users hit: text that looks identical can render as a full-file difference when the two sides came from different editors or platforms.
A concrete input and expected output from the current implementation.
Input
Left (original): Hello world This is a test Right (changed): Hello world This is a test!
Expected output
Row 1 shows 'Hello world' on both sides with no highlight. Row 2 is marked as changed on both sides. The right-hand line 'This is a test!' carries a character-level highlight on the trailing '!' marking it as added; the left-hand line 'This is a test' shows no character-level mark, because none of its characters were removed.
The two lines differ by exactly one appended character, so the line-level pass flags only the second row and the character-level pass inside that row isolates the difference to the final '!'. Every other character matches, so nothing else is highlighted.
The tool shows the two blocks in aligned rows and flags every row whose lines differ, then highlights the exact changed characters within each flagged row, so the mark lands on the edit itself instead of the whole line. Rows that match exactly stay unmarked, which keeps large files readable when only a few lines changed.
Every byte is significant: case, spacing, punctuation, and line endings all count. Content present in the right block but not the left is marked as added; content present in the left but not the right is marked as removed. Swapping the two inputs flips which side carries the additions, so the output always describes a left-to-right change.
No. The comparison runs entirely in the browser tab and the text never leaves the page, so pasting code, config, or other sensitive content is safe. Nothing is stored or transmitted, and closing the tab discards everything, which makes the tool usable for confidential snippets you would not paste into a server-side service.
The usual cause is invisible whitespace: trailing spaces, tabs where the other side has spaces, or CRLF versus LF line endings. The character-level highlight on a changed line reveals these extra characters. Normalize line endings and strip trailing whitespace from both inputs, then compare again.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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