Text Diff Checker
Paste two versions of a text to see which lines were added or removed.
- The quick brown fox
- jumps over the lazy dog
- leaps over the lazy dog
- Pack my box with five jugs
- Sphinx of black quartz
- Judge my vow, ten times
Lines with − were removed from the original; lines with + were added in the changed text. Unmarked lines are identical in both.
A text diff checker compares two blocks of text line by line and shows what changed. It marks lines that exist only in the changed version as added (+) and lines that exist only in the original as removed (−), leaving identical lines unmarked, then reports how many were added and removed.
What it does
Paste an original text on the left and a revised version on the right. The tool splits each block into lines and finds the longest run of lines the two versions share, so unchanged lines stay put. Anything left over is shown as a removed line (in the original but not the new text, prefixed −) or an added line (in the new text but not the original, prefixed +). A summary above the diff counts how many lines were added and removed.
How the comparison works
There is no formula — it is a deterministic procedure based on the longest common subsequence (LCS) of the two line lists. The tool builds a table of the longest sequence of lines that appears, in order, in both versions. Those matching lines are the anchors that stay unchanged; every other line is classified as added or removed by walking the table back through the two texts. Because it matches whole lines, a line that changes even slightly reads as one removal plus one addition.
- 1 Paste the original. Put the first version in the Original box — for example four lines of a paragraph you are editing.
- 2 Paste the changed version. Put the revised text in the Changed box. Keep line breaks where they are, since the comparison works line by line.
- 3 Read the marked lines. Lines prefixed − were in the original but dropped; lines prefixed + are new. Unmarked lines are identical in both versions.
- 4 Check the counts. The summary shows totals, e.g. “2 added, 1 removed”. A single reworded line shows as 1 removed and 1 added.
- 5 Copy the result. Use Copy diff to grab the whole comparison as plain text with + and − prefixes, ready to paste into notes or a message.
What the markers mean
How each line in the diff is labelled.
| Marker | Meaning | Where the line appears |
|---|---|---|
| (none) | Unchanged | Identical line, present in both versions |
| + | Added | In the changed text only — new since the original |
| − | Removed | In the original only — dropped in the changed text |
Line-level vs word-level
This is a line-level diff: it compares whole lines, so changing one word marks the entire line as removed and re-added rather than highlighting just the edited word. That keeps the output easy to scan for structural edits — added paragraphs, deleted sentences, reordered list items — and is the same model version-control tools use. A word-level diff would instead highlight the exact characters that changed within a line; for prose where you tweak wording inside long sentences, that can be more precise. Use this tool to spot which lines moved, appeared, or vanished; read the two versions side by side when you need to see a within-line wording change. It is handy for comparing drafts, spotting copy-paste changes, checking edits to config files or code snippets, and confirming what a collaborator altered.