DiffPoster

Paste a before/after snippet, get a shareable diff image. No login, no export dialog.

Before

After

Language

Everything runs in your browser. Nothing is uploaded or stored.

Paste code on the left and hit Generate.

Share a code change, not a screenshot

Diff Poster turns a before/after snippet into a single clean image of just the change. Paste the original code in one pane and the edited code in the other, pick the language, and it renders a token-level diff styled like a tidy editor window, sized 1200×675 for Twitter, Bluesky, and Slack previews. Copy it to your clipboard or download the PNG. The tokenizing, diffing, and image rendering all happen in your browser; nothing is uploaded.

Why token-level, not line-level

Most diff screenshots paint a whole changed line red or green. When you rewrite return 'hi ' + name; as return `hello, ${name}!`;, a line diff just says "this line changed" and hides what actually changed. Diff Poster diffs at the token level (identifiers, operators, literals, strings), so only the swapped tokens are marked. The reader sees the exact substitution, which is the whole reason to share the change.

How to use it

Paste the original code into Before, the edited code into After.
Choose JavaScript, Python, or plain text for syntax coloring.
Click Generate image.
Copy the image to your clipboard, or download the PNG.

FAQ

Is my code uploaded anywhere?: No. Every step runs in your browser. There is no backend and nothing is stored; close the tab and nothing is kept.
Which languages are supported?: Syntax coloring covers JavaScript and Python, plus a plain-text mode for anything else. The diff itself is language-agnostic, so plain text still highlights exactly which tokens changed.
How big can a snippet be?: It is built for function-sized changes, not whole files. A very large paste shows a size notice instead of freezing the tab, and a long snippet scales down or shows a "+N more lines" marker rather than cropping silently.
What size is the image?: 1200×675 pixels, the 16:9 frame Twitter, Bluesky, and Slack use for previews, rendered at your screen's pixel density so it stays crisp on retina displays.
Can I copy straight to my clipboard?: Yes, where the browser supports image clipboard writes. Where it doesn't, the Copy button is clearly disabled and Download PNG always works.