# no-undefined-server-variable

Disallow undefined server variables.

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



```mermaid
flowchart TD

root ==> ServersList --> Server --> ServerVariable

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

## API design principles

If a variable is declared but not defined, it's an error with the specification.

It is important to fix these errors to help clients consume APIs.

## Configuration

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


An example configuration:


```yaml
rules:
  no-undefined-server-variable: error
```

## Examples

Given this configuration:


```yaml
rules:
  no-undefined-server-variable: error
```

Example of **incorrect** server variables:


```yaml
servers:
  - url: 'https://{tenant}/api/v1'
```

Example of **correct** server variables:


```yaml
servers:
  - url: 'https://{tenant}/api/v1'
    variables:
      tenant:
        default: api.example.com
        description: Your server host
```

## 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-server-variables-empty-enum](/docs/cli/rules/oas/no-server-variables-empty-enum)


## Resources

- [Rule source](https://github.com/Redocly/redocly-cli/blob/main/packages/core/src/rules/oas3/no-undefined-server-variable.ts)
- [Server variable docs](https://redocly.com/docs/openapi-visual-reference/server-variables/)