Diff Checker

What is the Free Diff Checker?

The free Diff Checker compares two blocks of text or code side-by-side and shows exactly what changed — line by line. Paste your Original text in the left panel and the Modified version in the right panel. Added lines appear in green with a + prefix, removed lines in red with a − prefix, and unchanged lines in grey. A stats bar at the top counts total lines added, removed, and unchanged so you can gauge the scope of changes instantly.

• → Compare two versions of a code file to spot accidental or unexpected changes
• → Review edits to config files, SQL scripts, or JSON before deploying
• → Check what changed between two API responses or log outputs
• → Proofread two drafts of a document to find all textual differences
• → Verify that a find-and-replace operation only changed the intended lines

How to Use the Free Diff Checker

1. 1 Paste the original (before) version of your text or code into the Original panel on the left.
2. 2 Paste the modified (after) version into the Modified panel on the right.
3. 3 The diff output appears below — green lines (+) are additions, red lines (−) are deletions, and grey lines are unchanged.
4. 4 Read the stats bar: it shows the total count of added, removed, and unchanged lines at a glance.
5. 5 Toggle Show unchanged lines off to hide context lines and show only the differences — useful for large files with few changes.

Key Features

• 🟢
  Line-level diff

  Every added, removed, and unchanged line is clearly labelled with +, −, and space prefixes.
• 📊
  Change summary

  The stats bar shows the total lines added, removed, and unchanged at a glance.
• 👁️
  Hide unchanged lines

  Toggle off unchanged lines to focus only on the differences in large files.
• ⚡
  Instant comparison

  The diff updates as you type — no button press needed.
• 🔒
  Private comparison

  Your code and text never leave your browser. Safe for proprietary or confidential content.

Example Usage

Original: Hello World / Line two / Line three

Modified: Hello World / Line two edited / Line three / New line added

  Hello World
− Line two
+ Line two edited
  Line three
+ New line added

Frequently Asked Questions about the Free Diff Checker

What is the free Diff Checker?

Compare two pieces of code or text and highlight every difference.

Is the Diff Checker free to use?

Yes, the Diff Checker is completely free. No account, subscription, or signup is required — ever.

Does my data get uploaded anywhere?

No. The Diff Checker runs entirely in your browser. Your data is never sent to any server.

Does it work offline?

Yes. Once the page has loaded, the tool works without an internet connection.

Which browsers are supported?

All modern browsers — Chrome, Firefox, Safari, and Edge. No plugins or extensions required.

What diff algorithm does this tool use?

The tool uses the Longest Common Subsequence (LCS) algorithm — the same approach used by Unix diff, Git, and most professional diff tools. It finds the minimal set of changes needed to transform the original text into the modified version, producing clean and accurate results.

Can I compare code files, not just plain text?

Yes — paste any code (JavaScript, Python, SQL, JSON, YAML, CSS, HTML, etc.) directly into the panels. The tool compares line by line regardless of content type. Performance is capped at 500 lines per side to stay responsive in the browser.

Does the diff checker ignore whitespace differences?

Currently the comparison is exact — a line with a trailing space is treated as different from one without. If whitespace differences are creating noisy results, trim your inputs or normalise line endings before pasting.

Related Free Developer Utilities