Diff Checker
Paste an original text on the left and a changed version on the right to see exactly which lines were added, removed, or kept. The comparison runs line by line in your browser, so contracts, code, and config files never leave your device. Counts of added and removed lines update live as you type.
How it works
This diff checker compares two blocks of text line by line and shows which lines were added, which were removed, and which are unchanged. It computes the longest common subsequence of the two line lists, the same idea behind git diff, so the result is the minimal set of line additions and removals that turns the first text into the second.
Both inputs are compared inside your browser tab. Nothing is uploaded or stored, which matters for the things people actually diff: contracts before and after redlining, config files between environments, code snippets, and exported data. The counts of added and removed lines update live as you type or paste.
Two toggles change only the matching, never the displayed text. Ignore whitespace trims each line and collapses runs of spaces and tabs, so a re-indented file does not light up as fully changed. Ignore case lowercases lines before comparing, which helps with SQL keywords or HTML tags whose casing drifted.
How to use it
- Paste the original version of the text into the left box.
- Paste the changed version into the right box.
- Toggle ignore whitespace or ignore case if formatting noise is drowning out the real changes.
- Read the unified output: green lines with a plus were added, red lines with a minus were removed.
Worked examples
Input: Left: 'alpha\nbeta\ngamma' Right: 'alpha\nbeta\ndelta\ngamma'
Output: alpha and beta unchanged, '+ delta' shown as added before gamma. Summary reads +1 -0.
Input: Left: ' total = 5' Right: 'total = 5' with ignore whitespace on
Output: The line is reported unchanged, because leading spaces are trimmed before matching.
With the toggle off, the same pair shows one removal and one addition.
Edge cases and limits
- The diff is line-based, not character-based. A one-word edit inside a long paragraph marks the whole line as removed and re-added rather than highlighting the word.
- Inputs are capped at 1,500 lines each; longer texts are truncated for the comparison and a notice is shown.
- When several different edits produce equally minimal diffs, the tool picks one valid alignment, which may differ from another diff tool's output while still being correct.
- It compares plain text only. Word documents or PDFs need their text pasted in; formatting differences are invisible to it.
Common mistakes
- Diffing prose with hard line wraps. Re-wrapped paragraphs change every line boundary, so the whole text looks changed; unwrap lines first.
- Forgetting that trailing whitespace counts as a difference when the ignore whitespace toggle is off.
- Pasting the texts into the wrong sides and then misreading additions as removals. The left box is the before, the right box is the after.
Frequently asked questions
How does the diff checker compare two texts?+
It splits both texts into lines and finds the longest common subsequence between them. Lines present in both texts in the same order are marked unchanged, lines only in the first text are marked removed, and lines only in the second are marked added. This is the same line-based approach used by tools like git diff.
Is it safe to paste confidential documents or code?+
Yes. The comparison runs entirely in your browser with JavaScript. Neither text is uploaded, stored, or sent to any server, so private contracts, source code, and configuration files stay on your device.
Does the diff ignore whitespace or capitalization?+
You can toggle both. The ignore-whitespace option trims each line and collapses runs of spaces and tabs before comparing, and the ignore-case option lowercases lines first. The displayed text always shows your original input, only the matching logic changes.
Why does the whole line show as changed when I only edited one word?+
The comparison works on whole lines, like git diff without word-diff mode. Any change inside a line makes that line differ, so it appears once as removed and once as added. For prose, comparing sentence by sentence on separate lines gives a more readable result.
Can I diff two code files with different indentation styles?+
Yes. Turn on the ignore whitespace option so each line is trimmed and internal runs of spaces and tabs collapse before matching. Lines that differ only in indentation or alignment are then treated as unchanged, leaving real edits visible.
Related tools
More Text tools that run entirely in your browser.