Free Developer Tool — 100% Client-Side

Text Diff Checker

Name: Text Diff Checker - WebUtil
Author: WebUtil

Compare two texts side by side and highlight the differences between them.

Original Text

Changed Text

Diff Output

What Is a Text Diff?

A text diff (short for difference) is a comparison between two blocks of text that identifies what has been added, removed, or changed. A diff checker or diff tool performs this comparison automatically, line by line, and highlights the differences using color coding. Our free online text diff checker runs entirely in your browser so your data never leaves your machine.

Common Use Cases for Diff Tools

Code Reviews — Compare code changes between commits or pull requests to catch bugs and review modifications before merging.
Document Versioning — Track revisions in documentation, legal contracts, or academic papers across multiple drafts.
Configuration Management — Spot differences between configuration files across environments (dev, staging, production).
Data Migration Verification — Compare CSV exports, database dumps, or JSON payloads before and after data transformations.
Debugging — Isolate unexpected changes in log files, error traces, or generated output during troubleshooting.

How to Use This Text Diff Checker

Using this text comparison tool is simple. Paste your original text into the left textarea and your modified text into the right textarea. Click Compare to generate the diff. The output will display each line with a prefix: lines that match are shown with two spaces, added lines are prefixed with +, and removed lines are prefixed with -. Use the Copy button to copy the diff result to your clipboard.

Understanding Diff Output

The diff output uses clear visual cues. Lines shown in green with a + prefix are lines that appear only in the changed text — these are additions. Lines shown in red with a - prefix are lines that appear only in the original text — these are deletions. Lines with no color and two spaces are identical in both versions. When a line is modified, the original line appears in red and the new version appears in green. This line-by-line diff comparison makes it easy to spot exactly what changed at a glance.

Text diff checking is a fundamental diagnostic technique for identifying additions, deletions, and modifications between two versions of text or source code. Diff algorithms, historically pioneered by Eugene Myers and the Unix `diff` utility, compute the Longest Common Subsequence (LCS) to determine the minimal number of edit operations required to transform one string into another. Software developers, DevOps engineers, and technical editors rely on diff checkers daily to review code pull requests, audit configuration changes before deployment, compare JSON/XML API responses, and inspect contract or documentation revisions. A visual diff checker highlights inserted lines in green, deleted lines in red, and pinpoints exact inline character changes so subtle discrepancies—such as whitespace changes, altered port numbers, or swapped query parameters—are immediately obvious. WebUtil's Text Diff Checker runs entirely client-side: paste your original and modified text to inspect side-by-side or unified differences without uploading sensitive company data to third-party servers.

How to Do This in Code

import { diffChars } from 'diff';
const changes = diffChars(oldText, newText);
changes.forEach(part => {
  const color = part.added ? 'green' : part.removed ? 'red' : 'grey';
  console.log(`%c${part.value}`, `color: ${color}`);
});

import difflib
diff = difflib.unified_diff(old.splitlines(), new.splitlines(), lineterm='')
print('\n'.join(diff))

diff -u file1.txt file2.txt
# or with colordiff:
colordiff -u file1.txt file2.txt

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Related Guides & Tutorials

Text 5 min read

Text Diff Guide: Compare Texts and Find Differences Like a Developer

Learn how text diff checkers work for comparing code and documents, and how to interpret diff output.

Text Diff Checker FAQ

How does the text diff algorithm identify changes between two texts?

The diff engine calculates the Longest Common Subsequence (LCS) between the two inputs, identifying which lines were retained, added, or removed with minimal edit distance.

What is the difference between side-by-side and unified diff views?

A side-by-side view displays the original and modified texts in parallel columns. A unified diff combines both into a single linear view using + and - indicators.

Does this diff checker detect whitespace and indentation differences?

Yes. WebUtil highlights subtle whitespace changes, tab-versus-space differences, and newline alterations that frequently cause syntax bugs in code.

Is my sensitive code or document content uploaded to any server?

No. All text comparison executes locally on your device inside your browser's JavaScript sandbox. No content is ever sent over the network.

Can this tool compare structured data like JSON or YAML?

Yes. Paste two JSON payloads or YAML manifests to quickly spot differing keys, changed values, or missing properties.