Show HN: Codiff, a local diff review tool

A new app called Codiff just strutted onto Show HN promising to make it easier to review your own code changes before hitting commit — basically, a last-minute mirror check before your work goes public. It’s local, it’s pretty, it can add comments to specific changed lines, and it even has an optional AI walkthrough that explains what changed in plain language. On paper, that sounds like catnip for developers who are tired of squinting at cramped built-in tools.

But the real show was in the comments, where the mood swung from excited applause to instant side-eye. One early fan summed up the relief perfectly: reviewing changes inside a coding app has been “hard,” so this felt like a welcome rescue. Another commenter zoomed in on a painfully practical detail with a deadpan mic drop: “... for MacOS.” Ouch. In other words, nice toy — if you’re in Apple land.

Then came the classic internet twist: people immediately compared it to tools they already use. One person said Codiff oddly fills gaps even big-name apps like JetBrains still miss, especially simple things like searching files. Another basically shrugged and said, welcome to the pile, because everyone is building the same fix now. And the spiciest jab? A commenter mocked the whole AI era as a machine for recreating software that already exists, then name-dropped older tools like Kaleidoscope and File Merge like a veteran yelling, “Kids, we had this already!” It’s admiration, annoyance, déjà vu, and platform grumbling — all in one tiny launch thread.