Vercel’s firewall is more than just a basic protection layer; it’s a programmable shield that lets you define precisely what traffic is allowed into your application.
Let’s see it in action. Imagine you’re running an API that only accepts requests from a specific set of IP addresses. Here’s how you’d configure Vercel’s firewall to enforce that:
{
"version": 1,
"rules": [
{
"type": "allow",
"action": "allow",
"source": {
"ip": ["192.168.1.100", "10.0.0.5"]
},
"destination": {
"port": 8080
}
},
{
"type": "block",
"action": "block",
"source": {
"ip": ["0.0.0.0/0"]
},
"destination": {
"port": 8080
}
}
]
}
This JSON configuration, placed in your vercel.json file, defines two rules. The first rule explicitly allows traffic from 192.168.1.100 and 10.0.0.5 to port 8080. The second rule, crucially, blocks all other IP addresses (0.0.0.0/0) from reaching the same port. Vercel processes these rules in order, so any traffic not matched by the first allow rule will then be caught by the block rule.
The core problem Vercel’s firewall solves is providing granular control over network access to your deployed applications, moving beyond simple geographic blocking or basic WAF signatures. It empowers developers to implement security policies at the edge, directly within their deployment configuration. This means you can restrict access based on IP addresses, HTTP headers, and even request methods, all without needing to manage separate infrastructure for these rules.
Internally, Vercel’s Edge Network evaluates these rules against incoming requests before they reach your application code. When a request arrives, it’s inspected against the rules array in your vercel.json. The first rule that matches the request’s characteristics (source IP, destination port, headers, etc.) determines the action taken: allow or block. If no rules match, the default behavior is to allow the traffic.
You control this system by defining the rules array in your vercel.json. Each rule object has a type (either allow or block), an action (which is the same as type), a source object defining the criteria for matching incoming requests, and a destination object specifying where the traffic is headed. The source can specify ip addresses or CIDR ranges, and can also include headers for more sophisticated matching. The destination typically specifies a port.
A common misconception is that you need complex, external WAF solutions to achieve this level of control. However, Vercel’s firewall allows you to define these precise ingress policies directly within your project configuration. This means your security rules are versioned alongside your code, deployed automatically with your application, and managed through the familiar Vercel CLI or dashboard. It’s a declarative approach to network security that integrates seamlessly into the development workflow.
The next conceptual hurdle is understanding how to leverage request headers for even more fine-grained access control within your firewall rules.