Missing security headers in Vercel
mediumUpdated Oct 12, 2026
vercel.json can set the same headers. Do not set them twice in conflict.
Fix for Vercel
vercel.json can set the same headers. Do not set them twice in conflict. One place is enough. Preview deployments should get the same headers as production, minus a preload-level HSTS if previews move around.
The five-minute check, the other platforms, and the agent prompt are on the full guide. More Vercel fixes are on the Vercel page.