Diff Checker
Paste two pieces of text and see exactly what changed — added lines highlighted in green, removed in red. LCS-based diff, fully private.
Both texts are compared entirely in your browser — nothing is ever sent to a server.
How it works
- Paste your Original text in the left box and the Changed text in the right box.
- The diff updates automatically as you type — no button to press.
- Added lines are highlighted green (+), removed lines red (−), and unchanged lines are shown in muted text.
- A summary above the diff shows the total number of added and removed lines.
Frequently asked questions
- How does the diff algorithm work?
- The tool uses the Longest Common Subsequence (LCS) algorithm, the same approach used by Git and most diff utilities. It finds the largest set of lines that appear in both texts in the same order, then marks the remaining lines as added or removed.
- What do the colours mean?
- Green lines with a + gutter marker are lines that appear in the Changed text but not in the Original. Red lines with a − marker are lines present in the Original that are not in the Changed text. Unmarked lines are identical in both.
- Is this a word-level or line-level diff?
- This tool compares at the line level — it shows which lines were added or removed. For small intra-line differences, the context around the change makes it easy to spot what was altered.
- What is the +N / −M summary at the top?
- The summary counts show how many lines were added (+) and how many were removed (−) in total. A result with both counts at zero means the two texts are identical.
- Is my text stored or sent anywhere?
- No. The comparison is performed entirely in your browser in JavaScript. Neither text is ever transmitted to a server.