How to Automate PR Descriptions with GitHub Actions

What You'll Build

A GitHub Actions workflow that automatically calls the Runcept API on every pull request, generates a description from the diff, and posts it as a PR comment — no developer input required.

Prerequisites

Step 1 — Add Your API Key to GitHub Secrets

In your repo: Settings → Secrets and variables → Actions → New repository secret

Name: RUNCEPT_API_KEY

Value: your Runcept API key

Step 2 — Create the Workflow

Create .github/workflows/pr-description.yml:

name: AI PR Description
on:
  pull_request:
    types: [opened, synchronize]

jobs:
  describe:
    runs-on: ubuntu-latest
    permissions:
      pull-requests: write
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Get diff
        id: diff
        run: |
          DIFF=$(git diff origin/${{ github.base_ref }}...HEAD -- . ':(exclude)*.lock' | head -c 8000)
          echo "content<> $GITHUB_OUTPUT
          echo "$DIFF" >> $GITHUB_OUTPUT
          echo "EOF" >> $GITHUB_OUTPUT

      - name: Run agent
        id: agent
        run: |
          RESPONSE=$(curl -sS -X POST https://www.runcept.com/api/v1/run \
            -H "Authorization: Bearer ${{ secrets.RUNCEPT_API_KEY }}" \
            -H "Content-Type: application/json" \
            -d '{"agent": "pr-description", "input": {"diff": ${{ toJson(steps.diff.outputs.content) }}}}')
          JOB_ID=$(echo $RESPONSE | jq -r '.job_id')
          # Poll for result
          for i in {1..30}; do
            RESULT=$(curl -sS https://www.runcept.com/api/v1/jobs/$JOB_ID \
              -H "Authorization: Bearer ${{ secrets.RUNCEPT_API_KEY }}")
            STATUS=$(echo $RESULT | jq -r '.status')
            if [ "$STATUS" = "complete" ]; then
              echo "description=$(echo $RESULT | jq -r '.output.description')" >> $GITHUB_OUTPUT
              break
            fi
            sleep 3
          done

      - name: Post comment
        uses: actions/github-script@v7
        with:
          script: |
            github.rest.issues.createComment({
              issue_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
              body: ## AI-Generated Description\n\n${{ steps.agent.outputs.description }}
            })

Step 3 — Test It

Open a pull request. The workflow runs automatically and posts a comment within 30-60 seconds.

JavaScript Alternative

If you prefer a Node.js script instead of curl:

import { RunceptClient } from '@runcept/sdk'

const client = new RunceptClient({ apiKey: process.env.RUNCEPT_API_KEY })
const result = await client.run('pr-description', { diff: process.env.PR_DIFF })
console.log(result.output.description)

Next Steps

Use this agent on Runcept

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