Code reviews are an important part of the software development process, but they can also slow things down. Delays often happen when reviewers are busy, unavailable across time zones, or need to go through multiple rounds of feedback. This can make the review process feel repetitive and time-consuming. What if the first review pass could be handled by an intelligent assistant that works continuously, understands the codebase, and applies the team’s standards consistently?
That’s exactly what Gitlab’s Duo Agent Platform makes possible with its Code review foundational flow, it’s not just another AI suggestion tool, it’s an agentic system that runs inside your existing GitLab workflow, triggered by simple bot assignments or automated rules.
In this post, we’ll walk through how it works, why it’s a game-changer for modern teams, and how to set it up under 10 minutes.
Why Manual Code Reviews Slow You Down (And How AI Fixes it)
Traditional code reviews rely on human availability. A developer opens a MR, pings a couple of teammates, and then waits. Meanwhile, context gets lost, small issues slip through and velocity drops.
GitLab Duo’s Code Review flow flips the script. powered by Anthropic’s Calude 4.0 Sonnet (and compatible with self-hosted models), it acts like an always-on teammate.
When triggered, it
a) Analyzes every code change in the MR
b) Reads linked issues and existing discussion threads
c) Understands your repository structure and cross-file dependencies
d) Leaves detailed, actionable comments right in the MR
The best part is, it’s fully integrated, no copying code into another tool, no context switching. Everything happens inside GitLab’s interface.
Meet the Bot: @GitLabDuo as Your Automated Reviewer
The star of the show is the @GitLabDuo bot. Requesting a review is as easy as assigning it like any other reviewer:
a) Open your merge request
b) In the reviewer sidebar, add @GitLabDuo or drop a quick comment: /assign_reviewer @GitLabDuo
That’s it. The flow immediately starts a session (you can watch the progress in real time). Within minutes, you’ll see thoughtful comments appear strengths, critical issues, medium priority concerns, testing suggestions, security notes, and even an overall approval recommendation.
You can keep the conversation going too. Reply to any comment or mention @GitLabDuo in a thread with follow-up questions like “Can you suggest a more performant alternative?” or “Does this align with our error-handling standards?” The agent responds contextually, making reviews truly interactive.
Set It and Forget it: Automatic Reviews via Rules
The real power comes from full automation. GitLab lets you enable automatic reviews by GitLab Duo at three levels: Project (ideal for small teams), Group (great for organization), and Instance (for self-managed admins).
To enable it at the project level (Under 30 seconds)
a) Go to your project -> Settings -> Merge requests
b) Scroll to the GitLab Duo Code Review section
c) Enable “Enable automatic reviews by GitLab Duo“
d) Save changes
Every new MR will now automatically receive a first-pass review from @GitLabDuo. Settings cascade from instance -> Group -> Project. So you can enforce company-wide standards while giving teams flexibility.
Make the Bot Follow Your Rules: Custom Review
GitLab lets you define custom review instructions that the agent always respects.
Create a file in your repo:
.gitlab/duo/mr-review-instructions.yaml
This lets the bot focus on specific file types, skip areas like tests, enforce your internal coding style, highlight security or performance concerns, and respect architecture decisions that are special to your team
Ready to level up your reviews?
Automating the first pass of code reviews doesn’t replace human judgment, it multiplies it. With GitLab Duo’s Code Review flow, @GitLabDuo becomes the tireless junior reviewer that never misses a detail, while your senior engineers stay focused on what truly matters
Assign @GitLabDuo to your next MR and watch the magic happen
For more information on GitLab solutions, you can visit our website:
https://ecanarys.com/gitlab-solutions/
Or contact us at: gitlab@ecanarys.com