Transform rules are now available in vercel.json

You can now define transform rules in vercel.json to modify HTTP request and response headers or query parameters, without changing application code.

Unlimited transform rules are available for all customers, and let you:

• Set, append, or delete request headers, response headers, and query parameters

• Use conditional logic to apply changes based on request metadata

• Match by equality, inequality, prefixes, suffixes, inclusion in string arrays, or numeric comparisons for fine-grained control

This expands the flexibility of Vercel's CDN, which already supports routing behavior like redirects and rewrites to external origins.

For example:

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{
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  "$schema": "https://openapi.vercel.sh/vercel.json",
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  "routes": [
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    {
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      "src": "/(.*)",
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      "dest": "https://my-secure-proxied-dashboard.com/$1"
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      "transforms": [
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        {
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          "type": "request.headers",
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          "op": "set",
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          "target": {
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            "key": "x-using-vercel-cdn"
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          },
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          "args": "secret-value"
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        }
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      ]
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    }
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  ]
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}

Refer to the transform rules documentation for detailed examples.