Rules

Rules are used to enable a flag for a subset of users. Rules are evaluated from top to bottom. If a rule matches, the flag will return the configured value and stop evaluating the remaining rules.

See the example below.

Each rule has an attribute (1), a comparison operator (2), one or multiple targets (3) and an output value (4).

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Available Attributes

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Geolocation Attributes

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City

The city name for the location of the requester’s public IP address. Non-ASCII characters are encoded according to RFC3986.

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Country

Countries are identified by their ISO 3166-1 alpha-2 code.

We provide a list of many available countries as suggestions in the input component in the console.

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IP

The public IP address of the client that made the request.

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Region

A string of up to three characters containing the region-portion of the ISO 3166-2 code for the first level region associated with the requester’s public IP address.

Unfortunately, there is no official extensive list of available regions from Vercel.

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Custom Attribute

You can use custom attributes to enable a flag for a subset of users. For example, you can enable a flag for users with a specific userId or email.

Please refer to the API documentation for more information on how to set custom attributes.

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Comparison Operators

These are the available rule types. Each of them includes a small code snippet that shows the exact implementation for reference

value is the value of the attribute. target is what we compare the attribute value to.

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is in array

The rule will apply if the attribute is in the target array.

return target.includes(attribute);

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is not in array

The rule will apply if the attribute is not in the target array.

return !target.includes(attribute);

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contains

The rule will apply if the attribute contains the specified target.

return attribute.includes(target);

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does not contain

The rule will apply if the attribute value does not contain the specified target.

return !attribute.includes(target);

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equals

The rule will apply if the attribute value equals the specified targe.

return attribute === target;

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does not equal

The rule will apply if the attribute value does not equal the specified target.

return attribute !== target;

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is empty

The rule will apply if the attribute value is empty.

return attribute === "";

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is not empty

The rule will apply if the attribute value is not empty.

return attribute !== "";

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is greater than

The rule will apply if the attribute value is greater than the specified value.

return attribute > target;

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is greater than or equals

The rule will apply if the attribute value is greater than or equals the specified value.

return attribute >= target;

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is less than

The rule will apply if the attribute value is less than the specified value.

return attribute < target;

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is less than or equals

The rule will apply if the attribute value is less than or equals the specified value.

return attribute <= target;

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Example

The following flag will be evaluated for 80% of all users and enabled for those in Germany or the United Kingdom and for users with the attribute userId set to chronark.

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First Rule matches

Let’s assume our user is lucky enough to be chosen for the 80% and is located in Germany: The order of operations is as follows:

1. Evaluate percentage: ✅
2. Evaluate country: ✅ Since the user is located in Germany, and that is one of the countries specified in the rule, the value true will be returned.

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Any Rule matches

Our user is located in Norway and their userId is chronark, the order of operations is as follows:

1. Evaluate country: ❌
2. Evaluate userId: ✅

All rules will be avaluated until one of them matches. In this case, the flag will return true.

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Percentage fall through

Our user is not lucky enough to be chosen for the 80%:

In this case the rules will not be avalated and the flag returns false

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No rule hit

Lastly, let’s look at what happens if none of the rules match:

If your user is in the United States, and their username is not chronark:

1. Evaluate country: ❌
2. Evaluate userId: ❌

The flag will return false.