How Diff Checking Works
Diff algorithms compare two pieces of text and identify the minimal set of changes needed to transform one into the other. The most common approach is the Longest Common Subsequence (LCS) algorithm, which finds the longest sequence of lines (or characters) shared between both texts, then marks everything else as added or removed.
The output is typically displayed in one of two formats: unified diff (showing changes inline with + and - prefixes) or side-by-side diff (showing both versions in parallel columns with highlights). This tool uses a side-by-side view with color coding: green for additions, red for deletions, and yellow for modifications.
Line-level diffing catches which lines changed. Character-level diffing goes further, highlighting exactly which characters within a line were modified. This tool supports both, making it easy to spot even single-character typos in large blocks of text.
When You Need a Diff Checker
Code review without Git
Comparing two versions of a function or config file when you don't have access to version control. Paste the old and new versions to see exactly what changed.
Tracking document revisions
When a colleague sends you an "updated" contract or proposal, paste both versions to see precisely what was added, removed, or reworded. No more reading the whole thing again.
Debugging configuration changes
Something broke after a config update? Compare the working config with the current one to find the exact line that changed. Works for JSON, YAML, .env files, and any text format.
Tips for Effective Comparisons
Normalize whitespace before comparing
Trailing spaces and inconsistent indentation (tabs vs spaces) can create noise in your diff. If you only care about content changes, trim whitespace first or use the ignore-whitespace option.
Compare smaller chunks for clarity
Diffing an entire 5,000-line file can be overwhelming. If you know roughly where the change is, extract that section and compare just those lines for a cleaner result.
Use character-level diff for subtle changes
Line-level diff might show a whole line as "changed" when only one character is different. Character-level highlighting pinpoints the exact modification, which is useful for catching typos or off-by-one errors.
Limitations
- Compares plain text only. Cannot diff binary files, images, or structured documents (PDF, DOCX).
- Very large files (>1MB each) may cause the diff computation to take several seconds or freeze the browser.
- Character-level diff may be noisy for files with extensive changes. Line-level diff is better for large rewrites.
- Does not support three-way merge or conflict resolution — it only shows differences between two inputs.
Features
- Side-by-side and inline diff views
- Character-level change highlighting
- Line numbers for easy reference
- Any text format works: code, prose, config files, JSON, CSV
- Runs entirely in your browser. No data uploaded
- Free, no signup required
Frequently Asked Questions
What types of text can I compare?
Any plain text works: source code, configuration files, JSON, XML, Markdown, prose, CSV data, or even raw HTML. The tool compares text line by line regardless of format.
Is there a size limit for comparisons?
The tool runs in your browser, so there's no server-imposed limit. However, very large files (10,000+ lines) may take a moment to process and render. For best performance, compare sections rather than entire large files.
Can I ignore whitespace differences?
Yes. Whitespace-only changes (extra spaces, tabs vs spaces, trailing whitespace) can be filtered out so you only see meaningful content changes.
Is my text stored or sent to a server?
No. All comparison logic runs locally in your browser using JavaScript. Your text never leaves your device. Nothing is uploaded, stored, or logged.
How is this different from Git diff?
Git diff requires a repository and committed files. This tool lets you compare any two pieces of text instantly. No setup, no commits, no command line. Just paste and compare.
Last reviewed:
Your Privacy
All text comparison happens entirely in your browser. No data is uploaded to any server. Your files and their differences never leave your device.
In-Depth Guide
How Diff Algorithms Work: Myers, Patience, and Histogram
How modern diff algorithms actually work under the hood. Why git diff looks different from vimdiff, and when each approach produces better results.
Read guideTips & Related Workflows
- Format your JSON before diffing to make changes more readable; use the JSON Formatter.
- Write and preview Markdown changes side-by-side with the Markdown Editor.
- Count words in each version to see how much content changed with the Word Counter.
- Normalize text casing before comparing with the Case Converter.