# no-server-variables-empty-enum

Disallow server variables without enum list defined.

| OAS | Compatibility |
|  --- | --- |
| 2.0 | ❌ |
| 3.0 | ✅ |
| 3.1 | ✅ |



```mermaid
flowchart TD

root ==> ServersList --> Server --> ServerVariables

style ServerVariables fill:#codaf9,stroke:#0044d4,stroke-width:5px
```

## API design principles

If you use server variables, there are generally two kinds:

- tenant-driven
- environment-driven


In the case of environment-driven variables, you may want to predefine all of the possible values.

## Configuration

| Option | Type | Description |
|  --- | --- | --- |
| severity | string | Possible values: `off`, `warn`, `error`. Default `error` (in `recommended` configuration). |


An example configuration:


```yaml
rules:
  no-server-variables-empty-enum: error
```

## Examples

Given this configuration:


```yaml
rules:
  no-server-variables-empty-enum: error
```

Example of **incorrect** server variables:


```yaml
servers:
  - url: 'https://{env}.example.com/api/v1'
    variables:
      env:
        default: api
        description: Environment
```

Example of **correct** server:


```yaml
servers:
  - url: 'https://{env}.example.com/api/v1'
    variables:
      env:
        default: api
        description: Environment
        enum:
          - api
          - sandbox
          - qa
          - test
          - dev
```

## Related rules

- [no-empty-servers](/docs/cli/rules/oas/no-empty-servers)
- [no-server-example.com](/docs/cli/rules/oas/no-server-example-com)
- [no-undefined-server-variable](/docs/cli/rules/oas/no-undefined-server-variable)


## Resources

- [Rule source](https://github.com/Redocly/redocly-cli/blob/main/packages/core/src/rules/oas3/no-server-variables-empty-enum.ts)
- [Servers list docs](https://redocly.com/docs/openapi-visual-reference/servers/)