Text Diff Checker
Paste two versions of your text and instantly see what changed — added lines, removed lines, and everything in between.
Paste text in both panels and click Find Differences
What Is a Text Diff Checker?
A text diff checker is a tool that compares two versions of a document and highlights the differences between them. The word "diff" comes from the Unix diff command, a foundational tool used by software developers to track changes in source code. Today, diff tools are useful for anyone who works with text — writers, editors, developers, students, and researchers alike.
When you paste your original and modified texts into this tool, it performs a line-by-line comparison using an efficient algorithm. Each line is categorized as:
- Added — a new line present in the modified version but not in the original.
- Removed — a line that existed in the original but has been deleted in the modified version.
- Unchanged — identical lines that appear in both versions.
The result gives you an instant, color-coded overview of every change made, making it easy to review edits, track revisions, or audit modifications.
When Should You Use a Diff Checker?
Diff checkers solve a wide range of everyday text-comparison problems. Here are the most common use cases:
- Code Review: Quickly compare two versions of a script, configuration file, or code snippet to spot unintended changes before deploying.
- Document Editing: Track revisions between drafts of an essay, report, or legal document without relying on version-control software.
- Content Updates: See exactly what changed between two versions of a web page, blog post, or product description.
- Data Validation: Compare exported data files (CSV, JSON, plain text) to confirm that records match or identify discrepancies.
- Plagiarism Detection: Verify whether a submitted piece of writing differs sufficiently from a reference text.
- Configuration Management: Audit differences between environment config files (e.g.,
.env,nginx.conf,package.json) to troubleshoot deployment issues. - Translation Review: Align a translated document side by side with the original to ensure all sections have been translated.
How the Diff Algorithm Works
This tool uses a Longest Common Subsequence (LCS) algorithm — the same underlying approach used by classic diff utilities. Here is how it works:
- Split into lines: Both texts are split into individual lines.
- Compute LCS: The algorithm finds the longest sequence of lines that appear in both texts in the same relative order, without requiring them to be contiguous.
- Classify the rest: Lines in the original that are not part of the LCS are marked as removed; lines in the modified text that are not part of the LCS are marked as added; LCS lines are marked as unchanged.
- Render the diff: The result is displayed with color-coding — green for additions, red for removals, and neutral for unchanged lines — along with summary statistics.
The LCS approach produces a minimal, human-readable diff that accurately reflects how one text evolved from the other. It handles insertions, deletions, and re-orderings gracefully.
Frequently Asked Questions
Is my text stored or sent to a server?
No. This diff checker runs entirely in your browser using JavaScript. Your text is never sent to any server and is not stored anywhere. You can use it safely with confidential or sensitive documents. Once you close or refresh the tab, the data is gone.
How large can the texts be?
The tool handles texts of tens of thousands of lines comfortably in modern browsers. For very large files (hundreds of thousands of lines), performance depends on your device's processing power. For extremely large diffs, consider using a dedicated command-line tool such as diff on Linux/macOS or fc on Windows.
Does the diff checker compare word-by-word or line-by-line?
This tool performs a line-by-line comparison, which is the standard approach for most diff scenarios (code, configuration files, documents). Each line is treated as a single unit. If you need to compare individual words within a line, a word-diff tool would be more appropriate for that use case.
Are whitespace differences detected?
Yes. Each line is compared exactly as written, including leading and trailing whitespace. A line with extra spaces or different indentation will be flagged as a change. This is important for code and configuration files where indentation is meaningful.
What file types can I compare?
Any plain-text content can be compared: source code (JavaScript, Python, CSS, HTML, etc.), JSON, XML, Markdown, CSV, SQL, shell scripts, prose documents, and more. Simply copy and paste the text content into the panels — no file upload is required.