diff-checker.org

Free Online Diff Checker & Code Comparison Tool

Compare text, code, documents, files, and images instantly in your browser. Review changed lines, changed words, and changed pixels with private side-by-side or inline diff views.

🔒 Client-Side Browser Diff ⚡ No Sign-Up 📂 Multi-File 💻 Code Diff 🔗 Free to Embed 🖼️ Image Diff →
diff-checker.org mascot, a detective owl holding two clipboards comparing text

How diff-checker.org Works

1

Paste or Upload Two Versions

Paste the original and changed text, or upload text-based files such as source code, configs, documents, and notes. Add multiple files to compare project versions.

2

Choose a Diff Mode

Use word diff for prose, line diff for documents, character diff for fine detail, or code diff for a GitHub-style review view with line numbers.

3

See Every Change

Additions are highlighted in green and deletions in red. Review changes inline or side by side, then scan similarity, additions, and removals at a glance.

Why Choose diff-checker.org?

Code Diff Checker

Compare source code with line numbers, +/− indicators, and color-coded changes in a familiar review layout.

Image Diff Checker

Compare PNG, JPG, WebP, AVIF, GIF, and BMP images with slider, onion-skin, side-by-side, difference overlay, and flip views.

Multi-File Comparison

Upload multiple files at once. diff-checker.org matches files by name and opens each comparison in its own tab.

Word, Line & Character Diff

Switch between word-by-word, line-by-line, character-level, and code comparison modes for the right level of detail.

Private Browser Comparisons

Text, code, file, and image comparisons run in your browser, so pasted content and uploaded files stay on your device.

Free Diff Tool

No sign-up, no downloads, and no ads. Paste text, upload files, compare images, embed the widget, or call the public API for free.

Clear Change Statistics

See additions, deletions, unchanged segments, total changes, and an overall similarity percentage at a glance.

Large File Diff Performance

Designed for large text and code comparisons: benchmarked at 1M-line diffs in under a second and 5M-line diffs in seconds on desktop. Virtual scrolling keeps results responsive.

Use Cases

Code Review & Debugging

Compare source code versions to find changes between commits, branches, releases, or copied snippets. Works with JavaScript, Python, TypeScript, Java, Go, and 40+ text formats.

Visual QA & Image Review

Compare screenshots, UI mockups, exported designs, charts, and generated images to catch pixel changes before publishing.

Document & Essay Editing

Track differences between drafts of articles, essays, contracts, reports, and Markdown documents without installing desktop software.

Configuration Auditing

Compare .env files, YAML configs, JSON schemas, SQL, and infrastructure templates to catch unintended changes before deployment.

Project & Folder Comparison

Upload files from two project versions and review matched pairs in tabs, making multi-file changes easier to scan.

Embed diff-checker.org & Free API

Add diff-checker.org to your website, blog, or documentation in seconds. The same tool you see here is free to embed with no API key and no sign-up. Or call our public REST API directly.

📦 Embed as iframe

Drop this snippet into any HTML page. Works in WordPress, Notion, blogs, and docs. Want a different default mode, theme, or layout? Expand the customizer below for a live preview and a tailored snippet.

<iframe
  src="https://diff-checker.org/embed"
  width="100%"
  height="640"
  frameborder="0"
  loading="lazy"
  title="diff-checker.org · Free Diff Checker"
></iframe>
Customize & live preview defaults work for most embeds
Mode
Layout
Tabs
Background

🛠 REST API

POST https://diff-checker.org/api/diff. JSON in, JSON out. CORS open to all origins. Free to use.

curl -X POST https://diff-checker.org/api/diff \
  -H 'Content-Type: application/json' \
  -d '{
    "original": "Hello world",
    "modified": "Hello there world",
    "mode": "words"
  }'
Response shape 
{
  "mode": "words",
  "diffs": [
    { "type": "equal",   "value": "Hello" },
    { "type": "equal",   "value": " " },
    { "type": "added",   "value": "there" },
    { "type": "added",   "value": " " },
    { "type": "equal",   "value": "world" }
  ],
  "stats": { "added": 2, "removed": 0, "unchanged": 3, "total": 5 },
  "similarity": 60
}

Modes: words (default), lines, chars, code. Code mode also returns a codeLines array with line numbers.

Limits: 1 MB per side. For larger inputs, use the iframe (which runs entirely in the user's browser).

Open the embed view →

Supported File Types

Upload and compare source code, documents, configs, and common image formats. Text and code diff supports over 40 formats, and Image Diff supports PNG, JPG/JPEG, WebP, AVIF, GIF, and BMP.

JavaScriptTypeScriptPythonJavaGoRustC/C++RubyPHPSwiftHTMLCSSSCSSJSONYAMLTOMLXMLSQLMarkdownCSV.envDockerfileShellLuaDartKotlinVueSveltePNGJPG/JPEGWebPAVIFGIFBMP

Frequently Asked Questions

What is an online diff checker?

An online diff checker compares two versions of text, code, files, or images and highlights what changed so you can review differences quickly.

How do I compare two text files online?

Paste both versions into the comparison boxes or upload two text-based files. Choose a word, line, character, or code diff mode, then review the highlighted changes inline or side by side.

Can I compare two images online?

Yes. Open Image Diff to compare PNG, JPG, WebP, AVIF, GIF, or BMP images with slider, onion-skin, side-by-side, difference overlay, and flip views.

Is diff-checker.org free to use?

Yes. The browser diff checker is free to use with no sign-up and no ads. File uploads support text-based files up to 5 MB per file, and the public API accepts up to 1 MB per side.

Is my data private when I compare text, code, or images?

The main web tool, image diff tool, and iframe embed run comparisons in your browser, so pasted text, code, uploaded files, and images stay on your device. API calls are sent to the REST endpoint only to return the requested text diff.

Can I compare multiple files at once?

Yes. Upload multiple files to either side and diff-checker.org creates a tab for each matched filename, making it easier to review changes across a project.

How is code diff different from text diff?

Code diff shows a GitHub-style unified view with line numbers and +/− indicators, which is ideal for source code reviews. Text diff modes use inline highlighting that is better suited for prose, notes, and documents.

What file types can I compare?

You can compare 40+ text-based formats including JavaScript, TypeScript, Python, Java, Go, Rust, HTML, CSS, JSON, YAML, Markdown, SQL, shell scripts, and .env files. Image Diff supports PNG, JPG/JPEG, WebP, AVIF, GIF, and BMP.

Can I compare large files?

Yes. diff-checker.org is benchmarked at around 0.5 seconds for 200K-line diffs, under 1 second for 1M lines, a few seconds for 5M lines, and around 6 seconds for 10M lines on desktop. File uploads cap at 5 MB per file; for larger comparisons, paste directly. The public API caps at 1 MB per side.

Can I embed a diff checker on my own website?

Yes. diff-checker.org is free to embed via iframe, and the public REST API is free to call without an API key. See the "Embed & API" section for copy-paste snippets.

Ready to compare?

Scroll up, paste your text, upload files, or open Image Diff to find every change.