Diff Checker
Compare two blocks of text with color-coded diff highlighting. Side-by-side and inline views, word-level changes, and detailed statistics - all running privately in your browser.
Original Text
Modified Text
About Diff Checker
This free diff checker lets you compare two blocks of text and instantly see the differences. It uses a longest common subsequence (LCS) based diff algorithm to compute the minimal set of changes, then displays them with intuitive color coding.
Features
- Side-by-side view - Shows original and modified text in parallel columns with aligned line numbers.
- Inline view - Shows all changes in a single column with additions and deletions interleaved.
- Word-level diff - For modified lines, highlights the specific words that changed within each line.
- Color coding - Green for additions, red for deletions, yellow for modifications.
- Line numbers - Both views include line numbers for easy reference.
- Ignore whitespace - Option to treat lines differing only in whitespace as identical.
- Ignore case - Option to treat uppercase and lowercase as identical.
- Statistics - Summary of lines added, removed, modified, and unchanged.
- Copy diff output - Copy the unified diff format to your clipboard.
How It Works
The diff algorithm computes the longest common subsequence (LCS) of lines between the two texts. Lines present only in the original are marked as deletions, lines present only in the modified text are marked as additions, and lines that changed are marked as modifications with word-level highlighting showing the exact changes.
Hacker News Discussions
- Show HN: Secure private diffchecker with merge support 17 points · 16 comments
- Twitter Terms of Service Diff 230 points · 145 comments
- Twitter TOS Change 106 points · 64 comments
Source: Hacker News
Research Methodology
This diff checker tool was built after analyzing search patterns, user requirements, and existing solutions. We tested across Chrome, Firefox, Safari, and Edge. All processing runs client-side with zero data transmitted to external servers. Last reviewed March 19, 2026.
Community Questions
- How to compare two strings in JavaScript? 13 answers · tagged: javascript, string-comparison, diff
- Best diff algorithm for comparing text? 9 answers · tagged: algorithm, diff, text-comparison
- How does Git diff work internally? 7 answers · tagged: git, diff, algorithm
Performance Comparison
Benchmark: processing speed relative to alternatives. Higher is better.
PageSpeed Performance
Measured via Google Lighthouse. Single HTML file with zero external JS dependencies ensures fast load times.
npm Ecosystem
| Package | Description |
|---|---|
| diff | Text Diff |
| diff2html | Diff Viewer |
Data from npmjs.com. Updated March 2026.
Live Stats
How This Tool Works
The Diff Checker examines your input and produces a detailed analysis entirely within your browser. No data is sent to external servers, which keeps your information private and makes the tool work even when you are offline.
After you provide your input, the tool parses and validates it before running its analysis algorithms. Results are displayed in a clear, structured format with key findings highlighted. Depending on the tool, you may see tables, charts, status indicators, or annotated output that makes the analysis easy to interpret.
You can run multiple analyses in succession without any limits or cooldowns. Each analysis is independent, so you can compare results across different inputs by keeping previous outputs visible or by noting the key metrics.
Understanding the Results
The output is organized to present the most important findings first. Summary metrics or status indicators at the top give you an immediate answer, while detailed breakdowns below provide the context and specifics you need for deeper investigation.
Color coding and icons help you scan results quickly. Green typically indicates success or optimal values, yellow signals warnings or areas for attention, and red flags errors or critical issues. Hover over or click on individual items for expanded explanations where available.
If the tool provides scores or ratings, understand what scale they use and what constitutes a good versus poor result. The documentation on this page explains the scoring methodology and what actions you can take to improve your numbers.
Real World Use Cases
Developers and engineers use analysis tools to validate configurations, debug issues, and ensure compliance with standards before deploying changes. Catching problems early in a browser tool is faster and cheaper than discovering them in production.
Quality assurance professionals use these tools to verify that outputs from other systems meet expected specifications. A quick check in the browser can confirm or flag discrepancies without setting up a full test environment.
Students and learners use analysis tools to understand how systems work by examining real examples. Seeing a detailed breakdown of an input teaches concepts more effectively than reading a specification document alone.
Frequently Asked Questions
The diff checker uses a longest common subsequence (LCS) algorithm to find the minimal set of changes between two texts. It compares line by line and highlights additions, deletions, and modifications with color coding.
No. All comparison is performed entirely in your browser using JavaScript. No data ever leaves your device.
Green highlights indicate added lines or words, red highlights indicate deleted lines or words, and yellow highlights indicate modified lines with word-level changes shown within them.
Side-by-side view shows the original and modified text in two columns for easy comparison. Inline view shows all changes in a single column with additions and deletions interleaved.
When enabled, the diff checker treats lines that differ only in leading/trailing spaces, tabs, or multiple consecutive spaces as identical. This is useful for comparing code with different indentation styles.
When enabled, the diff checker treats uppercase and lowercase letters as identical. For example, "Hello" and "hello" would be considered the same.
When two lines are similar but not identical, the tool highlights the specific words that changed within each line, making it easy to spot the exact modifications without reading the entire line.
Yes. You can paste any text including source code, configuration files, JSON, XML, or plain text. The diff checker handles any text content with line numbers for easy reference.