For SEO purposes, it's necessary to ensure that you are not serving duplicate content, this means that you are not hosting the same content at more than a single URL.
Given the nature of Preview Deployments, and the way they are designed to give a realistic representation of a Production Deplpyment, they serve duplicate content by default. This article outlines how this case is handled by Vercel, to ensure your SEO ranking is not negatively impacted by duplicate content.
Vercel Preview Deployments will not be indexed by search engines because the
X-Robots-Tag HTTP header will be set as
noindex on every Preview Deployment. To confirm this, you can use the following curl (already available on most desktop devices) command in your terminal to check your Preview Deployment's headers:
curl -I <preview-deployment-url>
Amongst the output, you will find an
X-Robots-Tag header after executing the curl command.
Because all Preview Deployments have their
X-Robots-Tag header set to
noindex, search engine crawlers disregard them when indexing and applying SEO ranking algorithms.
If you believe your Preview Deployment is not showing the correct header, please contact Vercel Support using the support form available from the Vercel dashboard.