Text Diff Checker
Paste two versions of any text and instantly see every difference highlighted in color.
What is it?
A text diff checker is a tool that compares two versions of a document, piece of code, or any block of text and highlights exactly what has changed between them. The term "diff" comes from the Unix "diff" command, which has been a staple of software development since the 1970s — it shows you what lines were added, removed, or modified when going from one version of a file to another. This tool takes two text inputs — an original and a modified version — and applies a line-by-line difference algorithm to identify every change. Lines that were removed from the original are shown in red, lines that were added in the modified version are shown in green, and unchanged lines are shown in neutral color. This makes it immediately obvious what has been added or deleted without having to read both texts in full. The diff checker is useful in a wide range of scenarios: comparing two versions of a contract to find what clauses were added or removed, checking what changed in a configuration file after an update, reviewing edits made to a document by a colleague, comparing API responses between two versions of a service, or simply proofreading two versions of a text to find discrepancies. The result can be exported as a unified diff file — the standard format used by version control systems like Git.
How to use it
- Paste your original text into the left panel (labeled "Original").
- Paste the modified or new version of the text into the right panel (labeled "Modified").
- Click "Compare" to run the diff algorithm.
- Review the color-coded output: green lines were added, red lines were removed, and grey lines are unchanged.
- Check the summary above the diff for the total count of added and removed lines.
- Click "Export diff" to download the result as a unified diff file (.diff or .txt).
Why use this tool
Tracking what changed between two versions of a text manually is tedious, error-prone, and slow — especially for long documents. Whether you are reviewing a legal agreement, checking a configuration file, auditing a code change outside of a git workflow, or proofreading translated content, a visual diff tool immediately shows you the delta in a way your eyes can process efficiently. This tool runs entirely in your browser using a JavaScript implementation of the LCS (Longest Common Subsequence) algorithm — the same algorithm that powers git diff. No text is ever sent to a server, which is especially important when comparing sensitive documents like contracts, personal data records, or private code. You can use it offline once the page has loaded. The export function produces a standard unified diff format, which is compatible with any diff-viewing tool, code review platform, or version control system. This makes it easy to share the comparison with a colleague or store it for reference.
Frequently asked questions
What algorithm does this tool use?
The tool uses the LCS (Longest Common Subsequence) algorithm to compute the minimum set of changes between two texts. This is the same algorithm used by Unix diff and git diff. It compares line by line and identifies which lines are shared, which are only in the original, and which are only in the modified version.
Is there a length limit for the texts?
There is no hard limit. The diff is computed entirely in JavaScript in your browser. For very large texts (tens of thousands of lines), the computation may take a second or two. Texts of typical document or config file length compare instantly.
What does the exported diff file look like?
The export uses the unified diff format: lines starting with "+" are additions, lines starting with "-" are removals, and context lines are unchanged. This format is universally understood by code editors, review tools and version control systems.
Can I compare code files?
Yes. The tool compares any plain text content, including source code in any programming language, configuration files, JSON, YAML, CSV, XML, or prose text. Simply paste or upload the content of the files.
Are my texts sent to a server?
No. All processing happens entirely in your browser using JavaScript. Your texts never leave your device, making this tool safe to use with confidential contracts, private code, or sensitive data.