> For the complete documentation index, see [llms.txt](https://sevenval.gitbook.io/flat/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://sevenval.gitbook.io/flat/develop/reference/openapi-3/mocking.md).

# Mocking

OpenAPI allows to include *examples* in the API definition. FLAT uses [response examples](https://swagger.io/docs/specification/2-0/adding-examples/#responses) to implement an easy to use mock server.

Mocking can be activated by the client with the HTTP header

```
Mock: true
```

If given, FLAT will look for the `examples` of the API path's `200` `responses` section for an example with a content-type that matches the inbound `Accept` header.

[Mocked responses from upstream](/flat/develop/reference/openapi-6/upstream.md#mocking) work just the same way.

## Example

The [cookbook](/flat/develop/cookbook.md) has a recipe for the [built-in mocking](/flat/develop/cookbook/builtin-mocking.md).

## Configuration

To avoid accidentally running on mocks in production, mocking has to be explicitly activated with the `FLAT_ALLOW_MOCKING` environment variable (default `false`):

```
FLAT_ALLOW_MOCKING=true
```