Free Online Diff Checker Tool
Compare two texts side by side and instantly see additions, deletions, and modifications. Perfect for code reviews, document versioning, and tracking changes between file revisions.
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 — useful for catching typos or off-by-one errors.
Features
- Side-by-side and inline diff views
- Character-level change highlighting
- Line numbers for easy reference
- Supports any text format — 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.
Tips & Related Workflows
- Comparing JSON files? Format them first with our JSON Formatter.
- Check the word count of your documents with our Word Counter.
- Write and preview documentation in our Markdown Editor.