Diff Checker
Compare two blocks of text side by side and see every difference highlighted line by line. Added lines appear in green, removed lines in red, and unchanged lines in their default color. A summary bar shows the total count of additions, deletions, and unchanged lines so you can gauge the scope of changes at a glance. Use it to review code changes before committing, compare configuration files across environments, spot edits in legal documents or contracts, or verify that a migration script produced the expected output. The diff runs entirely in your browser using a Longest Common Subsequence algorithm — nothing is uploaded.
How to Use
- 1
Enter Original Text
Paste the original version of your text or code in the left panel. This is your baseline — the "before" state.
- 2
Enter Modified Text
Paste the modified version in the right panel. This is the "after" state you want to compare against the original.
- 3
Click Compare
Press Compare to run the diff algorithm. Added lines highlight in green, removed lines in red, and unchanged lines stay neutral. A summary bar shows total additions, deletions, and unchanged lines.
- 4
Review Changes
Scroll through the results to inspect each change. Use the color coding to quickly identify what was added, removed, or modified between versions.
Examples by Niche
Compare two versions of a function to see exactly which lines changed before approving a pull request or merging a branch.
Diff your staging and production nginx.conf, .env, or docker-compose.yml files to catch unintended differences between environments.
Compare draft and final versions of a blog post, legal document, or marketing copy to see every edit the reviewer made.
Compare API responses from two endpoints or two versions of the same endpoint to identify schema changes or data differences.
Frequently Asked Questions
What algorithm is used for comparison?
The tool uses a Longest Common Subsequence (LCS) algorithm to compute the optimal line-level diff. This is the same fundamental approach used by git diff and other professional diff tools, producing minimal and accurate change sets.
Can I compare files?
Paste the file contents into the two text areas. You can open files in any text editor, select all, copy, and paste into the tool. This works for code, config files, CSV data, JSON, or any plain text content.
Does it work with large files?
The tool handles files with thousands of lines without issues. For very large files (10,000+ lines), the comparison may take a moment since it runs in your browser. There is no server-side limit since nothing is uploaded.
What are common use cases for a diff checker?
Developers use it to review code changes outside of git, compare config files between staging and production, verify database migration outputs, and check API response changes between versions. Writers and editors use it to track revisions in documents and contracts.
Related Tools
AI Token Counter
Estimate token counts and API costs for GPT-4, Claude, and other AI models.
Regex Tester
Test regular expressions in real-time with match highlighting and capture group details.
HTML to Image
Render HTML and CSS code as a downloadable PNG image in your browser.
Timestamp Converter
Convert Unix timestamps to human-readable dates and vice versa with timezone support.
Cron Expression Generator
Build cron expressions visually with human-readable explanations and common presets.
API Tester
Test HTTP requests directly from your browser with custom headers, body, and response formatting.
Related Articles
7 Free Developer Utilities for Faster Debugging and Cleaner Code
Discover 7 free online developer utilities that speed up debugging, format messy data, and help you write cleaner code — no installs, no signups, all client-side.
Free Markdown Tools for Developers in 2026: Live Preview, Table Generator, and PDF Export
A practical guide to free online Markdown tools for developers and technical writers. Preview README files in real time, generate tables visually, and export Markdown to PDF — all without signups or data leaving your browser.
10 Free Online Developer Tools That Save Hours Every Week: QR Codes, Lorem Ipsum, Cron, and More
Discover 10 free online developer tools for QR codes, cron expressions, lorem ipsum, case conversion, API testing, CURL generation, and more. No signups required.
Free Online HTTP Request and API Debugging Tools: Complete Guide for Developers
Discover free browser-based tools for HTTP request testing, cURL conversion, JWT decoding, JSON formatting, and timestamp conversion. No signup, no installation, privacy-first.
Free SEO Writing Tools for Bloggers: Optimize Content Without Paid Subscriptions
A curated list of free SEO writing tools for bloggers and content creators — character counters, reading time estimators, keyword analyzers, and more. No signup required.
VSCode Keyboard Shortcuts: The Complete Reference Guide for Windows, Mac, and Linux
The complete VSCode keyboard shortcuts reference guide with over 120 shortcuts. Browse by category — editing, navigation, debugging, terminal — for Windows, Linux, and Mac.
The Complete TCP/UDP Port Numbers Reference: Essential Ports Every Developer and Sysadmin Should Know
A comprehensive, searchable reference of common TCP and UDP port numbers. Learn the most important ports for web, database, email, remote access, and development — with use cases and security notes.
30 Essential Free Online Developer Tools for Daily Coding Workflow
A curated list of 30 free online developer tools for JSON formatting, code generation, API testing, encoding, cryptography, and reference — all client-side, no signup required.
40+ Free Online Tools Every Remote Worker Should Bookmark in 2026
Discover 40+ free online tools for remote workers — password generators, timestamp converters, image compressors, color pickers, and more. No signups required.