Vercel Deploy Preview

Vercel Deploy Preview

Overview

Deploy preview environments for branches and pull requests. Every git push to a non-production branch generates a unique preview URL. Covers CLI-based previews, API-based previews, deployment protection, and comment integration.

Prerequisites

• Completed vercel-install-auth setup
• Project linked via vercel link
• Git repository connected in Vercel dashboard

Instructions

Step 1: Deploy Preview via CLI

# Deploy current directory to a preview URL (default — not --prod)
vercel

# Output:
# 🔗 Linked to your-team/my-app
# 🔍 Inspect: https://vercel.com/your-team/my-app/AbCdEfG
# ✅ Preview: https://my-app-git-feature-branch-your-team.vercel.app

# Deploy a specific directory
vercel ./dist

# Deploy and wait for build to complete (useful in CI)
vercel --no-wait  # returns immediately with deployment URL

Step 2: Deploy Preview via REST API

# Create a deployment via API — useful for custom CI pipelines
curl -X POST "https://api.vercel.com/v13/deployments" \
  -H "Authorization: Bearer $VERCEL_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "name": "my-app",
    "target": "preview",
    "gitSource": {
      "type": "github",
      "repoId": "123456789",
      "ref": "feature/new-feature",
      "sha": "abc123def456"
    }
  }'

Step 3: Check Deployment Status

# Poll deployment status until READY
curl -s -H "Authorization: Bearer $VERCEL_TOKEN" \
  "https://api.vercel.com/v13/deployments/dpl_xxxxxxxxxxxx" \
  | jq '{state: .state, url: .url, readyState: .readyState}'

# States: QUEUED → BUILDING → READY (or ERROR/CANCELED)

// Programmatic polling
async function waitForDeployment(client: VercelClient, deploymentId: string) {
  while (true) {
    const d = await client.getDeployment(deploymentId);
    if (d.state === 'READY') return d;
    if (d.state === 'ERROR' || d.state === 'CANCELED') {
      throw new Error(`Deployment ${d.state}: ${deploymentId}`);
    }
    await new Promise(r => setTimeout(r, 5000)); // poll every 5s
  }
}

Step 4: Configure Preview Environment Variables

# Add env vars scoped to preview only
vercel env add DATABASE_URL preview
# Enter value when prompted

# Or via API — scope to preview environment
curl -X POST "https://api.vercel.com/v9/projects/my-app/env" \
  -H "Authorization: Bearer $VERCEL_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "key": "DATABASE_URL",
    "value": "postgres://preview-db:5432/myapp",
    "type": "encrypted",
    "target": ["preview"]
  }'

Step 5: Deployment Protection

Vercel supports password-protecting preview deployments:

// vercel.json — require authentication for previews
{
  "deploymentProtection": {
    "preview": "vercel-authentication"
  }
}

Options:

• "vercel-authentication" — requires Vercel team login
• "standard-protection" — bypass for automation with x-vercel-protection-bypass header
• Disabled — previews are publicly accessible

Step 6: GitHub Integration — PR Comments

When a GitHub repo is connected, Vercel automatically:

1. Creates a preview deployment on every push
2. Posts a comment on the PR with the preview URL
3. Updates the GitHub commit status (pending → success/failure)
4. Adds "Visit Preview" link in the PR checks section

To configure in the Vercel dashboard:

• Settings > Git > Deploy Hooks for manual triggers
• Settings > Git > Ignored Build Step to skip builds for certain paths

# Ignored Build Step — skip deploy when only docs changed
# vercel.json
{
  "ignoreCommand": "git diff HEAD^ HEAD --quiet -- . ':!docs' ':!*.md'"
}

Preview URL Patterns

Output

• Preview deployment URL unique to each branch/commit
• Build logs accessible via Vercel dashboard or API
• PR comment with preview link (GitHub integration)
• Environment variables scoped to preview only

Error Handling

Examples

Verify a protected preview without leaking the bypass secret

Create a preview for a pull request, use a CI-held deployment-protection bypass token only in the automated smoke job, and request a harmless /health endpoint. Publish the preview URL and the commit SHA in the pull request, but never print the bypass header or token. Confirm the same URL is inaccessible without approved access, then expire the preview or retain it under the repository’s documented review window.

Resources

• Preview Deployments
• Deployment Protection
• CLI Deploy Command
• REST API: Create Deployment

Next Steps

For edge function development, see vercel-edge-functions.