CheckDiffs

Compare text & code before and after — private, in your browser.

Free forever for basic side-by-side compareNothing uploaded — runs in your browserPro TBD: export, ads-free, AI summary quota — basic stays free forever

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Private by design — verify it

Diffs run in your browser with Monaco. For basic side-by-side, your paste is not uploaded. Open DevTools → Network while you type to confirm — you should not see your content posted to our servers. Privacy details

Why we built this

About a month or two ago I was vibe coding with Gemini. New versions kept rewriting more than I asked, and long chats forgot earlier constraints. I wanted the simplest before/after compare in a browser — no account for basic use. Built by FT. Full story

FAQ

How do I compare two files or texts?: Paste the original on the left and the modified version on the right. Use Previous / Next to jump between changes. Pick a language for syntax highlighting if you are comparing code or JSON.
Is my text uploaded?: No — basic compare runs client-side in Monaco. Check the Network tab if you want proof.
Is CheckDiffs free?: Yes. Basic side-by-side is free forever, no account. Pro may later add export, ads-free UI, or an AI summary quota (TBD — no fake checkout).
Do you use my AI / code data for training?: No. We do not receive your pasted content for basic compare, so we cannot train on it. Optional AI summary features, if added later under Pro, will be called out clearly before anything is sent.
How do I review a code or text rewrite?: Paste the before version on the left and the after on the right — whether you edited it yourself, a teammate sent a rewrite, or you used a tool like ChatGPT, Claude, Cursor, Lovable, or Bolt. Use Previous / Next to walk each hunk. Nothing uploaded for basic compare.
What do red and green mean?: Red marks removals on the original side; green marks additions on the modified side. Counts appear above the editor.
Which languages are supported?: Plain Text, JavaScript, TypeScript, Python, HTML/CSS, SQL, and JSON via the selector — plus any text in Plain Text mode.