Text Diff Checker
Compare two texts and see exactly what changed, highlighted line by line with inline word differences. Free, instant and private — both texts are compared right in your browser and never uploaded.
How to use the Text Diff Checker
- Paste both versions. Put the original text in the left box and the changed text in the right box. Any text works — code, essays, configuration files, contracts or emails.
- Choose your options. Ignore case or whitespace if those changes do not matter, switch between a unified or side-by-side layout, and keep word-level highlighting on to see exactly which words changed inside a line.
- Compare and review. Press Compare texts to see removed lines in red and added lines in green, with counts of additions, deletions and a similarity score. Copy or download the result when you are done.
About this tool
This free text diff checker compares two blocks of text and highlights the differences line by line, the same way developers compare file versions. It uses a longest-common-subsequence algorithm to find the smallest set of changes, so matching lines stay aligned and only the genuine edits are marked. Inside a changed line it can also drill down to the word level, underlining just the words that were replaced rather than flagging the whole line. That makes it handy for proofreading two drafts, reviewing code changes, checking what a colleague edited in a document, or spotting an accidental change in a configuration file.
Everything runs locally in your browser — your two texts are never uploaded, stored or logged, so you can safely compare confidential documents, legal contracts, private source code or unpublished writing. There are no sign-ups, no watermarks and no length caps beyond your device's memory, and once the page has loaded it keeps working even offline.
Frequently asked questions
How does the comparison work?
The tool splits both texts into lines and finds their longest common subsequence — the largest set of lines that appear, in order, in both versions. Lines only in the original are shown as removed (red) and lines only in the changed text are shown as added (green). Everything in between is treated as an edit, which is why swapping a word can appear as one removed line and one added line with the changed words highlighted.
What is the difference between unified and side-by-side view?
Unified view stacks everything in a single column, with removed and added lines interleaved and marked by − and + — good for a compact overview. Side-by-side view puts the original on the left and the changed text on the right, aligning matching lines across the two columns so you can read both versions at once.
What do the ignore options do?
“Ignore case” treats Hello and hello as the same line. “Ignore leading/trailing spaces” ignores indentation and trailing spaces only. “Ignore all whitespace” ignores every space and tab inside the line, which is useful when only formatting changed. These options affect matching only — the diff still shows your text exactly as you typed it.
Is my text sent to a server?
No. The entire comparison happens in your browser using JavaScript. Neither text ever leaves your device, which makes this diff checker safe for private code, confidential contracts and sensitive documents.
Can it handle very large texts?
Yes, up to the limits of your device's memory. For extremely large inputs the tool automatically falls back to a simplified comparison and shows a notice, so it stays responsive instead of freezing your browser.