Compare two texts or code files side by side, then merge changes line by line
Diff Checker is a side-by-side compare and merge tool for text and code. It aligns matching lines with the Myers diff algorithm (the one Git uses), highlights the exact characters that changed, and lets you merge each change from one side to the other with undo, redo and reset. Both editors are sized like an A4 page so long files stay readable.
Paste or open the original on the left and the changed version on the right, then press Compare (or Ctrl/Cmd+Enter). Matching lines are aligned side by side, removed lines are red, added lines are green, and the exact characters that changed inside a line are highlighted. Everything runs in your browser.
Click a change to select it, then choose Keep Original, Keep Changed or Keep both. You can also use the arrow buttons in the middle gutter: the right arrow copies the left version across, the left arrow copies the right version back. Undo, redo and Reset let you back out of any merge.
Use the up and down buttons next to the change counter, or press Alt+Down and Alt+Up. The selected change is outlined and scrolled into view. The coloured ruler on the right edge shows where every change sits in the file; click a mark to jump straight to it.
Yes. Turn on Ignore whitespace to treat lines that differ only in spaces, tabs or indentation as equal, and Ignore case to treat upper and lower case as the same. Line endings (Windows CRLF versus Unix LF) are always treated as equal.
Both. Lines are aligned first using the same algorithm as Git (Myers diff), so an inserted line does not throw off the rest of the file. Inside each changed line you can highlight the differing words or individual characters with the Words and Chars switch.
Yes. Each side has Copy and Download buttons, and once every change is resolved both sides match and you can copy the result in one click. The .patch button downloads a standard unified diff that works with git apply and the patch command.
No. Files you open or drop are read by your browser and compared locally, so nothing is sent to a server. That makes it safe for source code, contracts and configuration files that contain private data. Files up to 5 MB can be opened.
No. Toolskyt operates under a zero-server policy. All calculations, data formatting, and file exports are executed locally on your machine.
No, this tool is 100% free. There are no limits, sign-ups, subscriptions, or hidden charges required.
Yes, absolutely. The tool executes 100% inside your local browser memory space. No inputs are sent to any servers.