Text Diff Checker — Free Online Side-by-Side Comparison Tool

Compare two texts side by side with color-coded added, removed, and unchanged lines. Live stats, unified diff output, and local history — runs entirely in your browser. This free online text diff checker runs entirely in your browser — no data is ever uploaded to a server.

About this tool

Text comparison (diffing) is an essential part of version control, editing, and content review workflows. This tool compares two texts side by side using a line-by-line diff algorithm that shows added lines in green, removed lines in red, and unchanged lines in neutral gray. It provides a summary with counts of added, removed, and unchanged lines so you can quickly assess the scope of changes.

While version control systems like Git have their own diff tools, this online diff checker is useful when you need to compare text without setting up a repository. It works entirely in your browser — no data is uploaded to any server — making it suitable for comparing sensitive documents, configuration files, or any text where privacy matters. The diff result can be copied for sharing in code reviews, documentation, or team communication.

Common Use Cases

  • Reviewing changes in code or documents before committing to version control
  • Comparing different versions of configuration files (Docker, Nginx, CI/CD) to identify what changed
  • Checking the difference between original and edited content for proofreading and editing
  • Verifying that automated transformations or search-and-replace operations produced the expected changes
  • Comparing data exports or CSV files to identify discrepancies between versions
  • Reviewing student submissions or peer edits against original documents

Pro Tips

  • Use the diff result summary (added/removed/unchanged counts) to quickly assess the scope of changes
  • Copy the diff output with the "Copy Diff" button to share formatted results in code review comments
  • Each diff line is stored in history, so you can revisit past comparisons without re-entering text
  • For large files, focus on sections with red (removed) and green (added) highlights rather than reading every line

Frequently Asked Questions

What algorithm does this diff tool use?

The tool uses a line-based longest common subsequence (LCS) algorithm to calculate the minimal edits needed to transform one text into another. This is the same approach used by version control systems.

Can I compare files instead of pasting text?

The tool accepts pasted text. For large files, you can open them in a text editor, select all, copy, and paste into the input areas. The tool processes everything in your browser with no file size limits beyond your device memory.

Is my data private when using this tool?

Yes. All text comparison happens entirely in your browser using JavaScript. No data is sent to any server, making this tool suitable for comparing sensitive or confidential documents.

What does a change shown on the same line mean?

The tool compares line by line. Changes within a single line (such as a corrected word) will appear as a removed line followed by an added line. For character-level diffs, you may need a specialized diff tool.

How to Use

1. Enter your input — type or paste your original text and changed text into the two boxes.

2. See live results — the tool updates instantly as you type.

3. Copy or download — copy the output to clipboard or download it.

4. History — your recent inputs are saved locally and can be pinned for quick access.

Example

Paste a sentence into Original and a lightly edited version into Changed. The tool highlights removed lines in red and added lines in green, updates the char/word/line stats in real time, and gives you a copyable unified diff.

Also check out the live tool at freeq.one/tools/diff — part of the FreeQ.One suite of free online tools.