Serve security.txt as text/plain with utf-8 on Vercel

Why it matters

RFC 9116 requires the file to be sent as text/plain in utf-8. Tools may reject it if the server labels it as html, binary or another charset.

The fix

1. Serve the file as a static file at public/.well-known/security.txt so Vercel sets the type from the extension. A route, rewrite or middleware that answers that path with html is the usual cause.
2. If you need to force the type, add a header rule to vercel.json, redeploy and check the response again.

{
  "headers": [
    {
      "source": "/.well-known/security.txt",
      "headers": [
        { "key": "Content-Type", "value": "text/plain; charset=utf-8" }
      ]
    }
  ]
}

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Related

• Reported by the security.txt check
• Publish a security.txt file
• Serve security.txt from /.well-known/
• Serve security.txt over https
• Add a Contact line to security.txt
• Fix the Contact value in security.txt
• Add an Expires line to security.txt
• Use an RFC 3339 date in the Expires line
• Renew the expired security.txt
• Renew security.txt before it expires
• Shorten the security.txt Expires date
• Fix repeated or insecure fields in security.txt
• Make the Canonical line match where the file is served