# no-empty-servers

Requires the `servers` list is defined in your API.

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



```mermaid
flowchart TD

root ==> ServersList

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

## API design principles

An empty `servers` list defaults to `localhost`, which is not practical for your API consumers.
An API cannot be used without a server.
Define servers so that the *Try it* and code sample generator features in OpenAPI tools (including Redocly) can produce functional API requests.

If you don't have a server because the consumer is responsible for setting up their own server, you can still describe the server with server variables.
The following code sample shows declaration of a server variable.


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

## Configuration

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


An example configuration:


```yaml
rules:
  no-empty-servers: error
```

## Examples

Given this configuration:


```yaml
rules:
  no-empty-servers: error
```

Example of **incorrect** empty servers:


```yaml
server: []
```

Example of **correct** servers:


```yaml
servers:
  - url: https://development.gigantic-server.com/v1
    description: Development server
```

## Related rules

- [no-server-example.com](/docs/cli/rules/oas/no-server-example-com)
- [no-server-trailing-slash](/docs/cli/rules/oas/no-server-trailing-slash)


## Resources

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