diff-review: a local pre-push code reviewer built for a friend

Uzain Ahmed — Sun, 04 Oct 2026 17:55:53 +0000

This is a submission for the Hacktoberfest Weekend Challenge: Build for a Friend

What I Built

diff-review is a small CLI and git pre-push hook. When you run git push, it grabs the diff, drops the noise (lockfiles, build output, binaries), sends it to an open-weight model through Ollama, and prints up to five short bullets about likely bugs, leftover debug code, and missing tests. Then your push continues.

It never blocks a push unless you opt in with --strict. If the model is offline, it prints "review skipped" and moves on.

I built it for a friend who is a developer and still getting comfortable with the terminal. He wanted a quick sanity check on his code before pushing, without sending it to a hosted service.

I showed it to him, and his feedback was honest: it would be better with a smarter model, and better still with a UI. The terminal-only setup is hard for him right now. I've put that in the "What's next" section below because it's the most useful thing I learned.

Demo

Code

uzainmalik123 / diff-review

diff-review

Local CLI and git pre-push hook that reviews your diff using an open-weight model running on your machine.

Example

diff-review · gemma3:1b via ollama · diff-file · 1 of 1 files · 142 lines
- src/api.ts: fetch result is used without checking response.ok
- src/api.ts: console.log left in getUser()

Why local and open-weight

Code never leaves your machine by default (Ollama runs locally). If you use OpenRouter, the diff is sent to that hosted service (see privacy note below).
Model is swappable via CLI flags, environment variables, or config; no code changes.
Free to run. Small 1B models give shallow reviews and are advisory only - they may miss things and sometimes produce unhelpful output. We also include rule-based checks plus model review (deterministic checks that catch obvious issues without invoking a model), and we honestly note that a 1B model adds little on top of those checks.

Quick

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View on GitHub

How I Built It

TypeScript on Node with zero runtime dependencies. I wrote a PRD and had OpenCode, an open-source coding agent, build the project from it. Then I tested it myself in a throwaway demo repo, including the case where the model is unreachable.

The default model is gemma3:1b, served locally by Ollama. The provider and model are config values, so you can point it at a bigger local model or at OpenRouter (the README documents the privacy tradeoff of sending the diff to a hosted service).

I picked a 1B model so it downloads quickly and runs on any laptop, and I'll be upfront about the cost: it's weak at code review. It misses subtle bugs and sometimes just echoes the prompt. The tool filters and formats its output to keep it short, but a 1B model can only do so much.

Why Does Open Innovation Matter?

Privacy: by default, the diff never leaves the machine. For a check on unreleased code, a closed API would mean sending it to a third party.

Swappable: the model is a config value, not a dependency. My friend's main complaint was model quality, and with an open setup the fix is changing one setting, not switching products.

Free and offline: no API key, no per-token cost, and it works without internet.

DEV Community: Uzain Ahmed