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How to add X-Frame-Options on Vercel

Last updated · Reviewed by a CISSP-certified security practitioner

To add X-Frame-Options on Vercel, set the header in vercel.json with the value DENY. Prevents your site being embedded in iframes (clickjacking). Commit and redeploy; headers apply on the next deployment. Then confirm it with curl -I or a free FixSecurityHeaders scan.

What does X-Frame-Options do?

X-Frame-Options (or the modern CSP frame-ancestors) tells browsers whether other sites may put your pages inside an iframe.

Risk if missing: Attackers can overlay your page invisibly and trick users into clicking buttons (clickjacking) — e.g. changing settings or confirming payments.

What is the Vercel configuration?

Add this to vercel.json:

vercel.json
{
  "headers": [
    {
      "source": "/(.*)",
      "headers": [
        {
          "key": "X-Frame-Options",
          "value": "DENY"
        }
      ]
    }
  ]
}

How do I add it step by step?

  1. Open vercel.json.
  2. Paste the X-Frame-Options configuration shown below.
  3. Commit and redeploy; headers apply on the next deployment.
  4. Run curl -I https://yourdomain.com and look for the x-frame-options line.
  5. Scan your site on FixSecurityHeaders to confirm the grade improved.

How do I verify it worked?

terminal
curl -sI https://yourdomain.com | grep -i "x-frame-options"
# expected:
# x-frame-options: DENY

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What are the common mistakes?

  • Use SAMEORIGIN if your own site frames its pages.
  • ALLOW-FROM is obsolete; use CSP frame-ancestors for allow-lists.
  • If CSP frame-ancestors is present, modern browsers ignore X-Frame-Options.
  • vercel.json headers don't apply to Next.js middleware responses — set them in next.config.js for Next apps.
  • The source pattern "/(.*)" matches every path.

Quick reference

HeaderX-Frame-Options
Recommended valueDENY
StackVercel
Wherevercel.json
ComplianceOWASP ASVS V14.4.7, NIST 800-171 3.13.1, CMMC SC.L2-3.13.1

FAQ

What value should I use for X-Frame-Options?

A safe default is DENY. Use SAMEORIGIN if your own site frames its pages.

Why isn't X-Frame-Options showing up on Vercel?

vercel.json headers don't apply to Next.js middleware responses — set them in next.config.js for Next apps. Also clear any CDN or page cache, and check you edited the config that actually serves your domain.

Does X-Frame-Options affect SEO or performance?

No measurable performance cost — it's a few bytes per response. It doesn't affect rankings directly, but a misconfigured policy can break page resources, so test before enforcing.

Which compliance frameworks reference X-Frame-Options?

OWASP ASVS V14.4.7, NIST 800-171 3.13.1, CMMC SC.L2-3.13.1.

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