Diff Checker

How to Use the Diff Checker

This free online diff checker compares two blocks of text and highlights the differences line by line. Paste your original text on the left and the modified version on the right, then click "Compare" to see an instant unified diff view. Lines that were removed are shown in red with a minus prefix, added lines appear in green with a plus prefix, and unchanged lines are shown without highlighting. All comparison is done entirely in your browser so your text is never uploaded to any server.

What is a Diff?

A diff (short for difference) is a comparison between two texts that shows what has changed between them. The concept originated in Unix with the diff command and is fundamental to version control systems like Git. Diffs are essential for code reviews, document editing, configuration management, and any workflow where tracking changes matters. This tool uses the Longest Common Subsequence (LCS) algorithm to produce an accurate, minimal diff output.

Common Use Cases

Developers use diff tools to compare code changes before committing, review pull requests, debug configuration file changes, and verify that automated edits were applied correctly. Writers and editors use diffs to track revisions in documents. System administrators compare configuration files between environments to find discrepancies. This tool handles any plain text including source code, configuration files, log files, and prose.

Tips for Better Comparisons

For the most readable results, make sure both texts use the same line ending style (LF vs CRLF). If comparing code, ensure consistent formatting first to avoid noise from whitespace differences. For large files, consider comparing specific sections rather than the entire file. The diff output can be scrolled vertically to review all changes, and the change count at the top gives you a quick summary of how many lines differ.

テキスト差分比較ツールについて

2つのテキストを行単位で比較し、追加・削除された行をハイライト表示するツールです。LCSアルゴリズムで正確な差分を算出します。コードレビューや設定ファイルの比較、ドキュメント修正の確認などに便利です。全ての処理はブラウザ内で完結します。