Diff Checker

Comparing two versions of text is one of the quickest ways to review edits, debug regressions, and validate migration results. This Diff Checker highlights added and removed lines instantly so you can focus on meaningful changes instead of scanning full files manually. For pattern-driven updates, test your expressions first in Regex Tester, then compare before and after output here. If your payloads are JSON, normalize structure in JSON Formatter before diffing so whitespace noise does not hide real changes. For content documentation workflows, pair final review with Markdown Preview.

How to Use

1. Paste the original text in the left editor.
2. Paste the modified text in the right editor.
3. Review highlighted additions, removals, and unchanged lines.
4. Toggle comparison options like ignoring whitespace or case.
5. Switch between split and unified output based on your review style.
6. Copy unified diff output for tickets, pull requests, or patch notes.

If the output is unexpectedly large, preprocess first: format JSON consistently, normalize line endings, and remove generated content where possible. This keeps the comparison actionable and easier to review.

Features

Visual Diff Display

See differences highlighted with colors:

• Green: Added lines (in modified text)
• Red: Removed lines (from original text)
• No highlight: Unchanged lines

Multiple View Modes

• Split View: See original and modified side by side
• Unified View: See all changes in a single column with +/- markers

Comparison Options

• Ignore whitespace: Treat multiple spaces as equal
• Ignore case: Compare case-insensitively
• Trim lines: Ignore leading/trailing whitespace

Diff Statistics

• Lines added
• Lines removed
• Lines unchanged
• Similarity percentage

Copy Unified Diff

Export your diff in standard unified diff format, compatible with git and other version control tools.

Use Cases

Code Review

Compare two versions of code to see what changed:

• Review pull requests
• Debug regression issues
• Track code evolution

Document Comparison

Compare drafts of documents:

• Legal contracts
• Technical specifications
• Content revisions

Configuration Files

Compare config files across environments:

• Development vs. production settings
• Before and after changes
• Template vs. actual values

Data Validation

Compare data exports or API responses:

• CSV/JSON data
• Database dumps
• API response validation

For JSON-heavy diffs, run each side through JSON Formatter first. For text replacements at scale, validate expressions in Regex Tester before running the transformation, then return here to verify the result. For documentation edits, use Markdown Preview as a final check to confirm rendered output matches intent.

Technical Details

This tool uses line-based comparison built on the Longest Common Subsequence approach to minimize noisy change sets and produce stable diffs for human review. In practical terms, it finds shared line sequences first, then marks lines outside that sequence as additions or removals.

Unified output follows standard patch notation with --- and +++ headers and prefixed lines (- removed, + added). That makes it convenient for issue trackers, changelogs, and workflows that need machine-readable diffs.

For best accuracy, normalize line endings and avoid mixing tabs/spaces across inputs unless formatting differences are part of the review target. Very large inputs can take longer because diff quality and speed are a trade-off; preserving readability typically matters more than raw compute time.

Understanding Diff Output

Split View

The split view shows both texts side by side:

• Left pane: Original text with removed lines highlighted in red
• Right pane: Modified text with added lines highlighted in green
• Line numbers shown for easy reference

Unified View

The unified view shows changes in a single stream:

• Lines starting with - were removed
• Lines starting with + were added
• Lines without prefix are unchanged

Unified Diff Format

The unified diff format is the standard for version control systems like Git:

--- Original
+++ Modified
 function greet(name) {
-  console.log("Hello, " + name);
+  console.log("Hi, " + name + "!");
   return true;
 }

This format can be:

• Applied as a patch using git apply
• Shared in code reviews
• Stored for documentation

Tips for Better Comparisons

Normalize Formatting First

If you’re comparing code, format both versions the same way first to focus on actual logic changes rather than whitespace differences.

Use Ignore Options Wisely

• Enable “Ignore whitespace” when formatting isn’t important
• Enable “Ignore case” for case-insensitive comparisons
• Enable “Trim lines” to ignore indentation differences

Large Files

For very large files (1000+ lines), the diff may take a moment to compute. The algorithm is optimized but complex diffs require more processing.

Algorithm

Our diff checker uses the Longest Common Subsequence (LCS) algorithm:

1. Find the longest sequence of lines that appear in both texts in the same order
2. Mark lines not in the LCS as added or removed
3. Calculate statistics based on the result

This produces optimal diffs that minimize the number of changes shown.

FAQ

What is the difference between split view and unified view?

Split view shows original and modified text side by side, while unified view combines changes in one stream with plus and minus markers.

Can I compare code safely in this browser tool?

Yes. Comparison runs locally in your browser, so pasted content is not sent to a remote server by default.

Why do whitespace-only changes create noisy diffs?

Line endings, indentation, and trailing spaces can all appear as edits. Enable ignore options when formatting differences are not meaningful.

When should I use regex testing before a diff?

Use regex testing first when you plan bulk find-and-replace changes. It helps validate patterns before comparing final output.

Privacy Note

All comparison happens in your browser. Your text is never sent to any server, making it safe to compare sensitive code or data.