How to Automatically Assign Reviewers in GitHub

Automating GitHub code reviews saves time, ensures balanced workloads, and keeps your team organized. Here's how you can do it:

1. Use CODEOWNERS: Automatically assign reviewers based on file paths or extensions. Example:

   /src/frontend/ @frontend-team
   *.js @javascript-developers
   

2. Enable Team Auto-Assignment: GitHub's built-in feature distributes reviews evenly across team members using round robin or load balancing.

3. Set Up GitHub Actions: Create workflows to assign reviewers dynamically based on file changes, labels, or conditional rules.

4. Enable Slack Notifications: Tools like PullNotifier send pull request updates directly to Slack, ensuring timely responses.

Why Automate?

• Faster Reviews: Cuts manual tasks and speeds up cycles.
• Balanced Workloads: Prevents reviewer burnout.
• Clear Accountability: Ensures ownership of code changes.

Quick Comparison

GitHub: How to Auto-Request PR Reviews with Code Owners

The following video walks through setting up CODEOWNERS for automatic pull request review assignment in GitHub:

GitHub Review Request Basics

GitHub's review request system plays a crucial role in effective code reviews. As teams grow and codebases become more complex, manually selecting reviewers can become inefficient and error-prone. This is where automation steps in to simplify the process.

Repository administrators can configure specific review requirements, such as setting a minimum number of approvals. However, managing these requirements manually can lead to delays and inefficiencies. Automation helps by ensuring reviewer notifications are sent promptly and consistently.

Why Automate Reviewer Assignments

Automating reviewer assignments shifts the review process from a tedious manual task to a smoother, more efficient workflow. Teams that adopt automated reviewer assignment systems commonly report several key benefits:

• Faster Reviews: Automatic notifications help speed up review cycles.
• Balanced Workloads: Automation ensures reviews are distributed evenly, reducing the risk of burnout.
• Improved Oversight: Team leads can track review progress more easily and spot potential delays.

Here’s a quick look at the main benefits of automated reviewer assignment:

Setting Up CODEOWNERS

GitHub's CODEOWNERS feature helps automate reviewer assignments by mapping file paths in your repository to specific team members or groups. Once set up, it ensures the right people are automatically notified to review changes in their areas, reducing manual effort and improving coverage.

How to Set Up a CODEOWNERS File

Follow these steps to configure your CODEOWNERS file:

1. File Location Place the CODEOWNERS file in one of these locations. GitHub searches in this order and uses the first one it finds:

   • .github/CODEOWNERS (highest priority)
   • Root directory (/CODEOWNERS)
   • docs/CODEOWNERS

2. Structure Example
   Define ownership rules using this format:

   /src/frontend/ @frontend-team
   *.js @javascript-developers
   

3. Verify the Setup
   Ensure the file:

   • Resides on your default branch
   • Uses UTF-8 encoding
   • Contains valid user or team names
   • Is accessible to specified reviewers

Common CODEOWNERS Patterns

Here are examples of typical ownership patterns:

Example: Here's what a typical CODEOWNERS file looks like for a project with separate compiler and documentation teams:

# Assign core team to compiler
/src/compiler/ @my-org/compiler-team
# Assign docs team to markdown files
*.md @my-org/docs-team

Tips for Effective Use

• Understand Last-Match-Wins CODEOWNERS uses a last-match-wins rule — when multiple patterns match a file, only the last matching pattern in the file determines the owner. Place your most general rules at the top and more specific rules at the bottom:

  # General fallback (first)
  * @maintainers
  # More specific overrides (last = wins)
  /src/auth/ @security-team
  

  If you reversed the order above, @maintainers would own everything including /src/auth/, because * would be the last match.

• Use Team-Based Assignments Assign entire areas to relevant teams:

  /.github/workflows/ @devops-team
  /docker/ @platform-engineering
  

• Protect Critical Files Add stricter review requirements for sensitive files:

  /config/ @senior-engineers
  package.json @lead-developers
  

Pairing CODEOWNERS with branch protection rules ensures that no changes are merged without the necessary reviews and approvals. To enable this, go to your repository's Settings > Branches > Branch protection rules, then check Require a pull request before merging and Require review from Code Owners. This setup strengthens code quality and safeguards critical areas of your project.

GitHub's Built-in Team Auto-Assignment

Before reaching for GitHub Actions, consider GitHub's native auto-assignment feature for teams. This is a built-in setting that automatically assigns individual team members when the team is requested for review, distributing reviews evenly across the team.

To enable it:

1. Go to your organization's Teams page and select the team.
2. Click Settings > Code review.
3. Enable Auto assignment and configure the number of reviewers to assign.
4. Choose between Round robin (rotates through members) or Load balance (assigns to members with the fewest recent reviews).

This feature works well when you want even distribution within a team that's already assigned via CODEOWNERS. For example, if CODEOWNERS assigns @my-org/frontend-team to a PR, auto-assignment can automatically pick 2 individual members from that team rather than notifying everyone.

GitHub Actions for Reviewer Assignment

GitHub Actions takes automation a step further by offering advanced tools for managing reviewer assignments. While CODEOWNERS and team auto-assignment handle most common scenarios, GitHub Actions allows for more dynamic options like conditional rules based on file changes, labels, or PR size.

Setting Up a Workflow File

To create a workflow file, you'll need:

• Event triggers for pull requests
• Job configurations with the necessary permissions
• Steps that define how reviewers are assigned

Here's a basic example:

name: Assign Reviewers
on:
  pull_request:
    types: [opened, ready_for_review]

permissions:
  pull-requests: write

jobs:
  assign:
    runs-on: ubuntu-latest
    steps:
      - uses: hkusu/review-assign-action@v1
        with:
          reviewers: "team-lead,senior-dev"
          max-num-of-reviewers: 2

This setup assigns up to two reviewers from the specified list. If you need more advanced rules, check out the example below.

Advanced Action Configuration

For more complex scenarios, here's an upgraded configuration that assigns different reviewers based on which files were changed:

name: Smart Review Assignment
on:
  pull_request:
    types: [opened, ready_for_review, labeled]

permissions:
  pull-requests: write

jobs:
  assign:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Check Changes
        id: changes
        run: |
          echo "frontend=$(git diff --name-only origin/${{ github.base_ref }}...HEAD | grep -c 'src/frontend' || true)" >> "$GITHUB_OUTPUT"
          echo "backend=$(git diff --name-only origin/${{ github.base_ref }}...HEAD | grep -c 'src/backend' || true)" >> "$GITHUB_OUTPUT"

      - name: Assign Frontend Reviewers
        if: steps.changes.outputs.frontend > 0
        uses: hkusu/review-assign-action@v1
        with:
          reviewers: ${{ vars.FRONTEND_REVIEWERS }}
          max-num-of-reviewers: 2
          bot-accounts: "dependabot[bot],renovate-bot"

      - name: Assign Backend Reviewers
        if: steps.changes.outputs.backend > 0
        uses: hkusu/review-assign-action@v1
        with:
          reviewers: ${{ vars.BACKEND_REVIEWERS }}
          max-num-of-reviewers: 2

A few important notes about this workflow:

• actions/checkout with fetch-depth: 0 is required so the runner has the full git history needed for git diff to compare branches.
• $GITHUB_OUTPUT is the current way to set step outputs in GitHub Actions (the older ::set-output syntax was deprecated in 2022 and removed in 2023).
• || true prevents the step from failing when grep finds zero matches (which returns exit code 1).

Teams using automated reviewer assignment workflows have reported significant reductions in PR cycle times, with quick reviewer notifications and balanced workloads playing a big role in this improvement.

For urgent updates or security fixes, you can apply priority-based rules:

- name: Emergency Review Assignment
  if: contains(github.event.pull_request.labels.*.name, 'urgent')
  uses: hkusu/review-assign-action@v1
  with:
    reviewers: "cto,security-lead"

Using PullNotifier for Review Management

Clear communication in Slack is just as important as automated reviewer assignments. While GitHub Actions handles assigning reviewers, managing notifications effectively is key to keeping review workflows running smoothly. PullNotifier simplifies this by sending pull request notifications directly to Slack, ensuring teams stay informed without drowning in unnecessary messages.

This tool makes sure reviewers see requests promptly. PullNotifier’s notification system offers several useful features:

Here’s how to set it up:

1. Initial Configuration
   Start by linking your GitHub repositories to Slack through PullNotifier.

2. Channel Mapping
   Assign specific repositories to Slack channels. This ensures that updates land in the correct channels, keeping communication organized - especially helpful for larger teams managing multiple projects.

3. User Association
   Match GitHub usernames with Slack handles. This step guarantees that when reviewers are assigned through GitHub Actions, they’re notified quickly in Slack.

PullNotifier’s simple setup and smart notification features make it easier to manage reviews efficiently without overwhelming your team. A 2-week free trial is available to get started.

Reviewer Assignment Tips

Assigning reviewers effectively requires thoughtful planning and regular updates to keep workflows running smoothly as your team grows or changes. Here are some strategies to help you fine-tune automated assignments over time.

Managing Review Workload

Use tools like repository-to-channel mapping to streamline notifications. For instance, PullNotifier can link repositories to specific Slack channels, ensuring review alerts are well-organized and sent to the right people. Pair this with GitHub's team auto-assignment (set to Load balance mode) to keep workloads even and manageable.

Maintaining Assignment Rules

Keep your CODEOWNERS file up to date to reflect changes in team roles. As your project evolves, make adjustments to ownership patterns, file paths, and team members — removing inactive contributors and adding new hires promptly. Remember that CODEOWNERS uses last-match-wins ordering, so review the pattern order whenever you add new rules. PullNotifier also offers customizable rules to automate notifications based on PR labels, authors, or reviewers, making it easier to manage assignments.

Conclusion

Automating reviewer assignments simplifies GitHub code reviews by integrating CODEOWNERS, team auto-assignment, GitHub Actions, and PullNotifier. This setup ensures pull requests are routed to the right reviewers automatically while sending timely Slack notifications. The process reduces the need for manual intervention and helps maintain consistent code review quality.

Teams using these automated workflows consistently report better review visibility, more balanced workloads, and stronger collaboration. By removing the friction of manual reviewer selection and ensuring timely notifications, the entire development cycle becomes more efficient — from pull request creation to merge.

FAQs