Text Diff Checker
Paste the original text on the left and the changed text on the right — differences appear below as you type.
Processed on your device — nothing is sent anywhere.
How it works
- Paste the original text into the left box.
- Paste the changed text into the right box. The comparison runs automatically as you type.
- Read the result below: lines removed from the original are marked with a minus on a red background, added lines with a plus on green, and unchanged lines stay gray.
Frequently asked questions
- How does the comparison work?
- The tool splits both texts into lines and computes a longest-common-subsequence diff, the same approach used by version-control tools like Git. It finds the largest set of lines the two texts share in order, then marks everything else as added or removed. This keeps the output short and easy to scan.
- Does it compare individual words or characters?
- No, the diff is line-based: a line counts as changed when it differs by even one character, and it is shown as one removed line plus one added line. Line-based output is usually the clearest way to review edits to code, configuration files or prose paragraphs.
- Is my text uploaded anywhere?
- No. Both texts are compared entirely in your browser with JavaScript — nothing is sent to a server, logged or stored. You can safely diff private notes, contracts or source code, and the tool keeps working offline once the page has loaded.
- Can I compare two versions of code or a config file?
- Yes. Paste the contents of each version into the two boxes — the line-based diff is exactly how programmers review code changes, so renamed variables, edited settings, and moved blocks all show up clearly. Whitespace differences count as changes, which is often exactly what you need to spot in indentation-sensitive files.
- Is there a limit on how much text I can compare?
- There is no fixed limit — documents of several thousand lines compare in well under a second on a typical machine. Because the diff runs locally, the practical ceiling is your device’s memory rather than a server quota. For extremely large files, trimming both texts to the relevant section keeps the output easier to read.
About this tool
This diff checker compares two pieces of text and shows exactly what changed between them. Paste the original version on the left and the edited version on the right; the tool aligns them line by line and highlights removals in red with a minus sign, additions in green with a plus, and leaves unchanged lines gray for context. The comparison reruns automatically on every keystroke, so you can fix a paste or tweak a line and see the result immediately.
The algorithm is the longest common subsequence diff — the same family of algorithm behind git diff and classic Unix diff. It finds the largest sequence of lines both texts share in order, and everything outside that sequence is reported as added or removed, which produces the shortest honest description of the change. All of it runs in your browser as JavaScript: neither text is transmitted, stored, or logged anywhere, so contracts, source code, and private notes are safe to compare, and the page keeps working offline once loaded.
Typical uses include reviewing edits a colleague made to a document, checking what changed between two versions of a configuration file, verifying that a rewritten paragraph kept the original meaning, comparing legal text or terms-of-service revisions, and spotting the one-character difference between a working and a broken snippet of code. Anywhere you would otherwise read two texts side by side hunting for differences, a diff does it in seconds.
For the clearest output, compare like with like: strip formatting artifacts before pasting, since a diff sees “smart quotes” and straight quotes as different characters. If a paragraph shows as fully removed and re-added, the texts probably differ in line wrapping rather than words — re-wrapping both the same way reveals the real edits. And when reviewing long documents, diff one section at a time so genuine changes are not buried in noise.