What is a Diff Checker?

A diff checker compares two pieces of text and shows exactly what changed between them. Lines that appear only in the original are marked as removed, lines that appear only in the modified version are marked as added, and lines that are identical remain unmarked. This makes it easy to spot edits, additions, and deletions at a glance — something that is almost impossible to do reliably by reading two long blocks of text side by side.

The word “diff” comes from the classic Unix diff command, and the idea is the backbone of version control: every time you review a change in Git, you are reading a diff. This tool brings the same capability to any two pieces of text, with no repository, no setup, and no command line — paste, compare, done. Everything runs in your browser, so the text never leaves your device.

How to Use the Diff Checker

Paste the original text into the left input area.
Paste the modified or newer version into the right input area.
The comparison runs automatically and highlights the differences.
Read removed lines in red and added lines in green; unchanged lines stay neutral.
Scroll through the result to review every change in order.

Common Use Cases

Code review — compare two versions of a file without a git setup.
Document editing — see what changed between draft v1 and v2.
Configuration files — spot differences between environments.
Data verification — confirm that two CSV exports match.
Translations — compare source and translated text side by side.

How the Comparison Works

The diff algorithm finds the Longest Common Subsequence (LCS) of lines between the two texts using a dynamic programming approach. Lines that are part of the LCS are shown as unchanged; everything outside the LCS is flagged as added or removed. This produces the minimal edit distance — the fewest changes needed to transform the original into the modified text.

Frequently Asked Questions

Is comparison case sensitive?

Yes. Lines that differ only in capitalisation are treated as different. Paste normalised text if you want a case-insensitive comparison.

Does this work with large files?

The tool handles thousands of lines efficiently in the browser. For very large files (tens of thousands of lines), consider using a native diff tool like git diff or diff on the command line.

Is my text sent to a server?

No. All comparison happens in your browser. Nothing is transmitted. Your text is private and never stored.