Text Diff Checker
See exactly what changed between two versions.
Runs entirely in your browser
Loading the tool…
- 0Added
- 0Removed
- 0Unchanged
- —Similarity
Paste two versions and every difference is marked: removed lines in red, added lines in green, and within a line that was edited rather than replaced, the individual words that changed.
The comparison uses Myers' algorithm, the same one behind git diff.
It finds the smallest set of changes that turns one text into the other,
which is why an inserted line shifts everything below it in a naive comparison but
not here: the rest of the file is correctly recognised as unchanged.
Ignoring case or whitespace changes only what counts as a difference; the text shown is always exactly what you pasted.
How to use it
- Paste the original on the left and the changed version on the right.
- Read the marked-up result: red is removed, green is added, highlights are the changed words.
- Switch between side-by-side and unified with the layout buttons.
- Turn on 'only show changes' for a long document, or ignore case and whitespace for a looser comparison.
Questions
Why is a diff tool better than reading both versions?
Because your eye skips over small changes. A one-character difference in a long line, a swapped digit, a trailing space: those are exactly what a diff catches and proofreading does not.
Side by side or unified?
Side by side puts the two versions in adjacent columns, which is easiest when lines were edited rather than moved, and it opens that way on a wide screen. Unified stacks them into one column with + and − markers; it is the default on a phone, because two columns of monospace text cannot be read at that width. Both mark exactly the same changes, so switch freely.
What does the similarity percentage mean?
The share of lines that are identical in both versions, counting both sides. 100% means the texts match; 0% means they have no line in common.
Can it compare files rather than pasted text?
Not directly. Open the files and paste their contents. Nothing you paste leaves your device, which is the trade for keeping the tool this simple.
Why do some lines show word highlights and others do not?
When a removed line is immediately followed by an added one, they are treated as an edit of the same line and compared word by word. A line with no counterpart is simply added or removed outright.
Is there a size limit?
Very large or completely unrelated texts stop at a cap, because the algorithm's memory grows with how different the two sides are. The page says so when it happens rather than freezing.
Your data stays on your device
Everything above runs inside your browser as WebAssembly compiled from Rust. Nothing you type is uploaded, logged or stored on a server. There is no server. You can load this page once, go offline, and it still works.