Automate GitHub PR Code Reviews with n8n and OpenAI

PR creation → extract code diffs → build review prompt → OpenAI generates comments → post back to PR with label

Who

Developers or DevOps engineers who want to automate code reviews for team GitHub repositories

You get

New PRs automatically trigger AI reviews; results posted as PR comments with optional ReviewedByAI label

You need

n8n · github

Steps

1. Import the workflow template

   In n8n, go to Workflows → Import from file or JSON, then paste or upload the workflow JSON file. After import, the canvas should show nodes including PR Trigger, HTTP Request, Code, AI Agent, and GitHub nodes.

2. Configure the GitHub trigger

   Select the PR Trigger node (GitHub Trigger), set the Repository to monitor and Events to pull_request. Choose GitHub OAuth2 for authentication, and ensure the githubOAuth2Api credential is already configured in n8n Credentials.

3. Fetch PR file diffs

   The template HTTP Request node "Get file's Diffs from PR" builds its URL from the upstream PR Trigger payload to fetch changed files/diff: `https://api.github.com/repos/{{$json.body.sender.login}}/{{$json.body.repository.name}}/pulls/{{$json.body.number}}/files`. Per workflow.json this node has **empty credentials and no authentication param**—the template does not attach a GitHub token/OAuth. That is not the same as "no auth needed in production": private repos will fail; public repos still face stricter unauthenticated GitHub rate limits. Applicability: only public repos within unauthenticated limits may work as shipped. Template defect risk: the URL uses `body.sender.login` as owner; sender is the actor who triggered the event (PR author/operator), not necessarily the repository owner (org repos / fork PRs break). Prefer something like `body.repository.owner.login` after verifying your webhook payload. Recommendation: add GitHub credentials to this HTTP Request (Authorization Bearer token or n8n GitHub cred) and fix the owner expression before using on real repos.

   Execution prompt · Source text。HTTP Request node URL field (Get file's Diffs from PR)

   Copy prompt

   =https://api.github.com/repos/{{$json.body.sender.login}}/{{$json.body.repository.name}}/pulls/{{$json.body.number}}/files

4. Build the review prompt with a Code node

   The Code node (Create target Prompt from PR Diffs) runs JavaScript to parse upstream diff data, format each diff with its filename, and assemble a structured prompt for the AI Agent. The output field is user_message.

   Execution prompt · Source text。Code node JS Code field (Create target Prompt from PR Diffs)

   Copy prompt

   const files = $input.all().map(item => item.json);
   
   let diffs = '';
   
   for (const file of files) {
     diffs += `### Fichier : ${file.filename}\n\n`;
   
     if (file.patch) {
       // IMPORTANT : On remplace tous les triple backticks par simple (ou échappement)
       const safePatch = file.patch.replace(/```/g, "''");
   
       diffs += "```diff\n";
       diffs += safePatch;
       diffs += "\n```\n";
     } else {
       diffs += "_Pas de patch disponible (probablement fichier binaire)._";
     }
   
     diffs += "\n---\n\n";
   }
   
   const userMessage = `
   You are a senior iOS developer. 
   Please review the following code changes in these files :
   
   ${diffs}
   
   ---
   
   Your mission:
   
   - Review the proposed code changes file by file and by significant modification.
   
   - Generate inline comments on the relevant lines of code.
   
   - Ignore files without patches.
   
   - Do not repeat the code snippet or the filename.
   
   - Write the comments directly, without introducing the context.
   `;
   
   return [
     {
       json: {
         user_message: userMessage.trim()
       }
     }
   ];

5. Configure OpenAI model and review agent

   In the OpenAI Chat Model node, select a model (e.g., gpt-4o-mini, gpt-4o, gpt-4-turbo, or gpt-4) and configure the openAiApi credential. In the Code Review Agent node (AI Agent), set promptType to define and set text to reference the upstream Code node's user_message. The Agent connects to OpenAI via ai_languageModel and optionally to Code Best Practices (Google Sheets) via ai_tool.

6. Post comment and add label

   The GitHub Robot node uses the GitHub API to post the AI-generated review ($json.output) as a comment on the current PR. Then the Add Label to PR node adds a ReviewedByAI label to the PR (label text is customizable). Both nodes require githubApi or githubOAuth2Api credentials; repository and PR number dynamically reference the PR Trigger.

7. Configure team code guidelines lookup (optional)

   To let the AI reference team coding guidelines, enable the Code Best Practices node (Google Sheets Tool). Prepare guidelines with descriptions and good/bad examples in a Google Sheet, then configure the node with: OAuth2 credential, document URL, and sheet name. This node connects as a tool to the Code Review Agent and can be queried during review generation. Other databases or tools can replace Google Sheets.

You are an n8n workflow setup assistant. The user wants to replicate the "GitHub PR automated AI code review" template. Assist in this order:
1) Confirm the user has an n8n instance, GitHub repo admin access, and an OpenAI API Key;
2) Guide them to import workflow.json and verify all nodes are present;
3) Walk through credential setup (openAiApi, githubOAuth2Api, githubApi, optional googleSheetsOAuth2Api);
4) Remind them the Code node's default persona is "senior iOS developer" and should be edited for other stacks;
5) Suggest testing with a sample PR to verify triggering, diff fetching, comment posting, and labeling.