Introducing GitBot: An Open-Source AI Code Reviewer for GitLab

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Code reviews are often the main bottleneck in software engineering. We all know the struggle. You wait days for a review only to get comments about missing semicolons or variable naming while the actual architectural risks go unnoticed.

While GitHub users have seen a lot of new AI tooling recently, the GitLab ecosystem often relies on manual checks or expensive enterprise add-ons. This is especially true for companies running self-hosted instances.

That is why I built GitBot. It is a lightweight, open-source Node.js application that connects your GitLab Merge Requests to Gemini AI for instant, intelligent code reviews.


 


Why I Built This (And Why I Didn't Use n8n)

When I first scoped this project, my instinct was to use n8n, a low-code workflow automation tool. It seemed simple enough. I just needed a webhook to trigger on a Merge Request, send a prompt to the AI, and post a comment.

But as soon as I dug into the requirements, I hit a wall of complexity regarding efficiency and context.

I realized that a basic automation would re-review the entire file every time a developer pushed a small fix. To make this tool actually useful and cost-effective, I needed Smart Incremental Logic.

The app needs to check the MR version history and make a decision:

  1. Version 1: Is this the first draft? If so, fetch the full file content to give a comprehensive review.

  2. Version > 1: Is this a follow-up fix? If so, fetch only the comparison between the previous commit and the new one.

Implementing this conditional logic involved fetching versions, comparing commit SHAs, and handling edge cases where an "Update" event is just a title change vs. a code push. Doing this in a visual editor would have resulted in a massive, unmaintainable web of nodes.

By switching to a Node.js backend, I could write clean functions to handle this orchestration efficiently. Sometimes "Low Code" turns into more work than actual code.

What GitBot Does

This isn't just a wrapper around ChatGPT. It is engineered to be a helpful teammate.

  • Precise Inline Comments: It doesn't just dump a summary at the end. It comments on the specific line of code that needs attention.

  • Smart Incremental Reviews: If you push a fix, GitBot only reviews the new code. It ignores the stuff it already approved.

  • Context Aware: It calculates line numbers dynamically so comments land exactly where they should.

  • Privacy-First: You bring your own API key. No third-party SaaS holding your code data.

How to Deploy

I designed this for simplicity. It is a standard Node.js app.

  1. Clone the repository.

  2. Set your .env variables (GitLab Token, Gemini API Key).

  3. Run it (Docker or npm start).

  4. Add the Webhook URL to your GitLab Project settings.

That is it. Your MRs are now getting instant feedback.

Open Source for the Community

This project is 100% Open Source. If your company uses GitLab and you want to speed up your review cycles without breaking the bank, check out the repo

 

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