Why is there a warning after I download?
The page cannot confirm that your browser finished saving the download, and Download B does not save changes in A. Check your saved file and keep anything you need from A before leaving.
A LITTLE HELP FOR YOUR NEXT CHANGE
Compare. Review.
Keep your work.
Start with two versions of a file. Compare Code shows their differences and lets you choose which changes to keep, all in your browser.
From two files to your result
- Open or paste both versions. Put your reference in A and your result in B. Both fields are editable. Opening a file selects a language; the language setting applies to both fields.
- Choose a difference. Use the Differences list or Previous/Next. Use A → B copies the selected block into B. Keep B marks a block reviewed without changing its text.
- Review your changes. Undo and Redo affect B. Ctrl/Cmd+Z works in the focused editor. All A → B replaces the complete result and can be undone.
- Save and check. Set the result filename and choose Download B. Open the downloaded file again to check it. Download B saves only B; keep any edits to A separately.
Only changes folds unchanged sections. Show spaces & tabs makes whitespace visible without changing it. Code size and Wrap lines adjust the view. Focus mode gives the editors more room while preserving both texts and their history.
What syntax checking covers
Checks run automatically after edits for supported languages. You can also select Check syntax and click a reported location to jump to it.
| Language | Check available |
|---|---|
| JavaScript / JSX | Syntax parsing; code is not executed. |
| TypeScript / TSX | Syntax parsing without type checking. |
| JSON | JSON syntax. |
| YAML | Syntax without schema validation. |
| Python | Preliminary grammar and indentation checks; verify the result with Python itself. |
| HTML, CSS, Java, C/C++, SQL, Markdown | Highlighting only. |
Each side is checked as a complete file, so an incomplete snippet can produce errors. Clean syntax does not prove correct logic, working imports or a safe program. Compare Code does not run or automatically repair your code.
Files and limits
- Open UTF-8 text files up to 512 KiB (524,288 bytes) per file.
- Each editor supports up to 200,000 UTF-16 text units and 4,000 lines. Some emoji and other characters use two text units.
- Downloads preserve the original LF, CRLF or CR line endings, mixed line endings and UTF-8 BOM. New lines you type use that file's main line-ending style.
- Comparison includes spaces, tabs and the final newline. Large differences may be grouped into broader blocks.
The workspace compares two texts. It does not compare folders or whole projects, connect to Git repositories, or perform a three-way merge.
Common questions
Can I recover a closed session?
No automatic recovery is available. Text and editing history live in the open tab. Save your work before closing, reloading or clearing the workspace.
Why won't my file open?
Check the file size, line count and encoding. Save it as UTF-8 text first. Binary files and files over the stated limits are not supported.
Copy B is unavailable, or formatting changed.
Your browser may restrict clipboard access. Download B instead, or select and copy B manually. Clipboard transfers may alter line endings; downloading preserves them.
Syntax checking is incomplete.
Choose a supported language and try Check syntax again. If checking remains unavailable, save both texts before reloading the page. Treat an incomplete check as unverified.
Does the website work offline?
It needs a connection to load its files. Comparison and syntax checks then run locally. Reloading or opening a new page offline is not guaranteed.
Report a problem
Use the project's GitHub issues. Include your browser and operating system, the steps to reproduce the problem, what you expected and what happened. A small invented example is usually enough.
Issues are public. Remove private code, credentials and personal data from examples or screenshots before posting. The application does not send a report for you. See Privacy for details about local processing and website requests.