You change one line in a config file, and a site stops working. Which line was it? A diff checker answers that question in seconds. Kwebby's Diff Checker takes two versions of a text, finds every difference and highlights it: additions in green and removals in red, with unchanged content left plain. Paste the original, paste the changed version, click Compare and read the result. It works for code, documents, configuration files and any other plain text.
Key Takeaways
- Kwebby's Diff Checker compares an Original Text with a Changed Text and highlights added content in green and removed content in red, and leaves unchanged content plain.
- It has two views: Line mode highlights whole changed lines, and Word mode highlights only the changed words within a line.
- Ignore whitespace and Ignore case options hide differences that do not matter to you.
- The comparison runs in your browser, so your text is not sent to a server. It is free and needs no account.
- Diff is old and well tested. It was part of the 5th Edition of Unix in 1974, and its operation is based on solving the longest common subsequence problem.
- Git builds on the same idea. Its
git diffcommand shows changes between the working tree, the index, commits and files on disk. - A diff shows what changed, not whether the change is correct. You still need to review it.
What Is the Kwebby Diff Checker?
The Kwebby Diff Checker is a free web tool that compares two pieces of text and highlights the differences. You paste the original into the Original Text box and the new version into the Changed Text box, then click Compare. The result shows every addition, deletion and change in one highlighted view, with counts of removed and added lines at the top.
The word "diff" comes from the Unix command that reports the differences between two files. The online version applies the same idea to text you paste, so you do not need a terminal, a repository or a desktop app.
Key Features and How It Works
The tool has two input boxes, a Compare button, Swap and Clear buttons, two view modes, two options and a color-coded result.
Original Text and Changed Text
The Original Text box takes the earlier version. The Changed Text box takes the later one. Keeping them in that order matters: additions mean new content in the changed version, and removals mean content that was only in the original.
The Compare Button
Click Compare to run the comparison. The tool then shows a highlighted diff of every addition, deletion and change. Edit texts takes you back to the input boxes, Swap exchanges the two texts, and Clear empties both. If the texts match, the tool says they are identical.
Color-Coded Results
Added lines are green and marked +, removed lines are red and marked -, and unchanged lines have no highlight. You can scan a long file and look only at the colored parts.
Line Mode and Word Mode
Line mode highlights whole lines that changed. If one word in a line is different, the old line is shown in red and the new line in green. Word mode merges each changed line into one row marked ~, with removed words struck through in red and added words in green. That is easier to read when the edits are small, such as a changed number in a long sentence. You can switch modes before or after you click Compare.
Ignore Whitespace and Ignore Case
Ignore whitespace treats lines as equal when they differ only in spaces, tabs or indentation. Ignore case treats "Hello" and "hello" as the same. Both options start switched off.
Browser-Only and Free
The comparison runs in your browser, so the texts are not sent to Kwebby. The tool is free, and it also has Share buttons and a "Report if not working" link.
How a Diff Works
A diff is a list of the smallest set of edits that turns one text into the other. Wikipedia's article on the diff command explains that its operation is based on solving the longest common subsequence problem: it finds the longest run of content the two files share in the same order, then reports everything outside that run as added or deleted.
Command-line tools print the result in set formats. In unified format, a plus sign precedes added lines, a minus sign precedes deleted lines, and unchanged lines are preceded by a space. Kwebby's tool shows the same symbols and adds colors.
Developers meet diffs in version control daily. Git's diff documentation describes git diff as showing changes between the working tree and the index, between two commits, or between two files on disk. For a project with history, use Git. For a quick check of two pasted snippets, an online diff checker is faster.
How to Use the Diff Checker
Comparing two texts takes five steps.
- Paste the original. Put the earlier version in the Original Text box.
- Paste the changed version. Put the later version in the Changed Text box.
- Click Compare. The highlighted diff appears.
- Pick Line mode or Word mode. Use Line mode for a quick overview and Word mode when edits are small. Tick Ignore whitespace or Ignore case if those differences do not matter.
- Review each change. Read the green and red sections, and check that every difference is intended.
Best Practices for Comparing Text
A diff is only as clean as the inputs. These habits keep the result readable.
Compare Like With Like
Different line endings, tabs versus spaces and trailing spaces can make unchanged lines look different. If a whole file lights up red and green, tick Ignore whitespace and compare again. Line endings are already handled, so Windows and Unix line breaks compare as equal.
Choose the Right Mode
Use line mode to see the shape of a change across a long file. Switch to word mode when you suspect a small edit hidden inside a long line, such as a changed value, a typo or a swapped word.
Keep Inputs in the Right Order
Always paste the older version on the left and the newer on the right. Reversing them turns additions into deletions. If you pasted them the wrong way round, click Swap.
Do Not Compare Minified Code
A minified file is a single very long line, so any change marks the whole line. Compare the readable source files instead, and minify afterwards with the JS Minifier.
Compare in Pieces
For very large files, split the content into sections and compare them one by one. The result is easier to review, and you are less likely to miss a change. If two long texts differ in many places, the browser may not be able to compare them in one go, and the tool asks you to compare smaller sections.
Treat Sensitive Text With Care
The tool compares the texts in your browser. Even so, avoid pasting passwords, API keys and private customer data into any online tool.
Use Version Control for Real Projects
An online diff checker is for ad hoc checks. For code that lives in a repository, commit often and use git diff so the history is kept with the project.
Common Use Cases
- Code review. Compare code before and after a refactor to check that only the intended changes were made.
- Document revisions. See what changed between versions of contracts, policies, articles and reports, even without track-changes features.
- Configuration files. Compare server configs, JSON files or environment settings across dev, staging and production to find differences.
- Content verification. Check that copied content was not accidentally modified, or that a translation keeps the same structure.
- SEO content updates. Compare a page before and after an optimization to document what you added or removed.
- Data checks. Compare an API response with the expected output.
Related Kwebby Tools
The Diff Checker is part of our Text Tools collection. These tools help with the files you compare:
- XML to JSON converts XML into JSON so you can compare data in one format.
- CSV to JSON converts CSV data into JSON for comparison.
- Plagiarism Checker checks content against web sources, which is a different job from comparing two files you already have.
- Remove Duplicate Lines cleans repeated lines from lists before you compare them.
- Line Counter counts the lines in each version.
- JS Minifier compresses JavaScript after you finish comparing the readable source.
Frequently Asked Questions (FAQs)
What is a diff checker?
A diff checker compares two texts and highlights what is different between them. It marks added content in green and removed content in red, and leaves unchanged content plain, so you can see what changed between two versions of a document, code file or any text.
What is a diff checker used for?
People use it for code review, document revision tracking, configuration file comparison and content verification. It also helps with SEO content updates and checking that translations or copies match their source.
What is the difference between line mode and word mode?
Line mode highlights entire lines that changed, so one different word marks the whole line. Word mode highlights only the changed words within a line, with removed words struck through. Word mode is better for small edits, and Line mode is better for an overview.
How does a diff work?
A diff finds the longest common subsequence of the two texts, the longest run of content they share in the same order. Everything outside that shared run is reported as added or removed. Unix diff and Git use the same core idea.
Can I compare code with this tool?
Yes. Paste two versions of any code into the boxes and click Compare. For code in a repository, git diff also shows changes along with commit history.
Is the Diff Checker free?
Yes. It is free, needs no account and runs in your browser. Paste your two texts and click Compare.
Final Thoughts
When something changes and you do not know what, a diff gives you an answer. Paste the old and new versions into the Diff Checker, read the green and red lines, and switch between line and word mode until the change is clear. Next time you edit a config file or a draft, save a copy first. Then you can compare the two in seconds and catch the one line that did not belong.