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Response headers

Last updated November 6, 2025

The following headers are included in Vercel deployment responses and indicate certain factors of the environment. These headers can be viewed from the Browser's Dev Tools or using an HTTP client such as .

Used to specify directives for caching mechanisms in both the Network layer cache and the browser cache. See the Cache Control Headers section for more detail.

If you use this header to instruct the CDN to cache data, such as with the directive, Vercel returns the following header to the client:

-

An integer that indicates the number of bytes in the response.

The media type that describes the nature and format of the response.

A timestamp indicating when the response was generated.

Shows where the request came from. This header can be overridden by other proxies (e.g., Cloudflare).

A header often abbreviated as HSTS that tells browsers that the resource should only be requested over HTTPS. The default value is (2 years)

Present only on:

We add this header automatically with a value of to prevent search engines from crawling your Preview Deployments and outdated Production Deployments, which could cause them to penalize your site for duplicate content.

You can prevent this header from being added to your Preview Deployment by:

The header is primarily used to indicate the cache status of static assets and responses from Vercel's CDN. For dynamic routes and fetch requests that utilize the Vercel Data Cache, this header will often show even if the data is being served from the Data Cache. Use custom headers or runtime logs to determine if a fetch response was served from the Data Cache.

The following values are possible when the content being served is static or uses a Cache-Control header:

The response was not found in the cache and was fetched from the origin server.