Diff Checker

Compare text, code, PDF and Word files side by side in a private diff checker. Runs locally and works offline.

Diff Checker shows two versions of anything side by side and marks what was added, removed or edited. Paste two snippets, drop in two documents, or pick two open tabs. The result updates as you type. It all runs in your browser, so nothing you check leaves your computer. 🚀 How it works 1. Click the toolbar icon. The tool opens in a new tab. 2. Put the original on the left and the new version on the right, or load a document into each panel. 3. Green lines were added, red lines were removed. Edit either panel and the highlighting follows. ✍️ Writing and editing Use it as a text comparison tool for drafts, contracts or translations. Edited phrases are highlighted inside each paragraph, so you can check the difference between a template and a filled-in copy, or see what an editor touched in your draft. 💻 Code and data The editor is Monaco, the same one VS Code uses, and it picks syntax highlighting for 17+ languages on its own. Review a patch before you commit it, run a JSON compare on two API responses, or read through XML configs and SQL dumps. Prettier formatting, sorted JSON keys and Ignore Whitespace hide the noise that doesn't matter. 📁 Documents File comparison works with PDF, Word (.docx) and Excel (.xlsx), plus plain text and source code, up to 50 MB each. Content is extracted on your machine. Spreadsheets turn into tables, so a modified cell is easy to spot. Anything over 10 MB switches to a faster algorithm. 🗂 Browser tabs Pick two open tabs, say staging and production, and see how their page source differs. 👀 Layout • split or unified view, with scrolling kept in sync • hide unchanged lines, or revert a single block with one click • swap the panels, copy the result or clear a panel • dark and light themes that follow your system • the keyboard shortcuts and undo you know from an IDE 🕘 History The last 50 comparisons stay on your device. Open an old one, delete it, or clear the list. 🤖 AI summary (optional) If you add your own OpenAI API key, you get a short summary of the edits in plain language. The default model is GPT-6 Luna; for long or tricky revisions you can switch to a stronger one such as GPT-6.1 Sol. The feature stays off until you turn it on. Only then is text sent to OpenAI, and the key is kept in local storage. 🔒 Privacy It works offline. There is no account, and nothing you paste is stored on a server or logged. You get the convenience of an online diff checker without uploading anything. ❓ Questions 📌 How to compare two Word documents? Drop one .docx on the left and the other on the right. Each edit is highlighted. 📌 How to compare two Excel files? Add both .xlsx files. Each sheet becomes a table and modified cells are marked. 📌 Can I hide formatting noise? Yes. Turn on Ignore Whitespace, or press Format before you read the result. 👉 Install the extension and see what's new in any revision within seconds.