Developer

Diff Checker — Free 2026

Compare two blocks of text and see additions, removals and changes highlighted side by side.

Original Text

Modified Text

Diff Result

Lines Added

Lines Removed

Unchanged

How It Works

Paste your original text
Paste your modified text
View the differences

Why Use a Diff Checker?

Comparing two versions of a file is one of the most common tasks in software development, content editing, and document management. A diff checker visually highlights exactly what changed between two texts, saving you from reading through hundreds of lines to spot a single modification. Whether you are reviewing pull requests, comparing configuration files, or tracking edits in a legal document, a diff tool makes the process fast and reliable.

How Line-by-Line Diffing Works

This tool uses the Longest Common Subsequence (LCS) algorithm, the same fundamental approach used by Git and Unix diff. It finds the longest sequence of lines that appear in both texts in the same order. Any line not part of this common subsequence is classified as either an addition (present only in the modified text) or a removal (present only in the original). The result is a clear, color-coded view of every change.

Common Use Cases

Developers use diff checkers to review code changes before committing. Writers compare document drafts to track editorial revisions. System administrators diff configuration files to audit changes on servers. If you need to validate the structure of a changed file, try our JSON formatter alongside this tool. For counting the words in your updated text, use the word counter.

Frequently Asked Questions

What is a diff checker?

A diff checker is a tool that compares two blocks of text and highlights the differences between them. Lines that were added, removed, or changed are visually distinguished with colors, making it easy to spot changes at a glance.

How does the diff algorithm work?

This tool uses a Longest Common Subsequence (LCS) algorithm to find the optimal alignment between the two texts. Lines present only in the original are marked as removed, lines only in the modified text are marked as added, and matching lines are left unchanged.

Can I compare code files with this tool?

Yes. Paste any two blocks of text including source code, configuration files, or documents. The tool performs a line-by-line comparison and works with any programming language or plain text format.

Is my text sent to a server?

No. All processing happens entirely in your browser using JavaScript. Your text never leaves your device, making this tool completely private and safe for sensitive content.