# Generate Clients

As **FastAPI** is based on the OpenAPI specification, you get automatic compatibility with many tools, including the automatic API docs (provided by Swagger UI).

One particular advantage that is not necessarily obvious is that you can **generate clients** (sometimes called <abbr title="Software Development Kits">**SDKs**</abbr> ) for your API, for many different **programming languages**.

## OpenAPI Client Generators

			},
			expectErr: "--etcd-servers-overrides invalid, must be of format: group/resource#servers, where servers are URLs, semicolon separated",
		},
		{
			name: "test when encryption-provider-config-automatic-reload is invalid",
			testOptions: &EtcdOptions{
				StorageConfig: storagebackend.Config{
					Type:   "etcd3",
					Prefix: "/registry",
					Transport: storagebackend.TransportConfig{

```JSON
{"message": "Hello World"}
```

### Interactive API docs

Now go to <a href="http://127.0.0.1:8000/docs" class="external-link" target="_blank">http://127.0.0.1:8000/docs</a>.

You will see the automatic interactive API documentation (provided by <a href="https://github.com/swagger-api/swagger-ui" class="external-link" target="_blank">Swagger UI</a>):

![Swagger UI](https://fastapi.tiangolo.com/img/index/index-01-swagger-ui-simple.png)

* `/items/`
* `/items/{item_id}`

...as we intended.

* They will be marked with a list of tags that contain a single string `"items"`.
    * These "tags" are especially useful for the automatic interactive documentation systems (using OpenAPI).
* All of them will include the predefined `responses`.
* All these *path operations* will have the list of `dependencies` evaluated/executed before them.

        // In contrast to `ClasspathRootsResolver.addModularRoots`, we do not need to handle automatic Java modules because JDK modules
        // aren't automatic.
        return javaModuleGraph.getAllDependencies(javaModuleFinder.computeDefaultRootModules()).flatMap { moduleName ->

<img src="/img/tutorial/behind-a-proxy/image03.png">

!!! tip
    The docs UI will interact with the server that you select.

### Disable automatic server from `root_path`

If you don't want **FastAPI** to include an automatic server using the `root_path`, you can use the parameter `root_path_in_servers=False`:

```Python hl_lines="9"
{!../../../docs_src/behind_a_proxy/tutorial004.py!}
```

		return nil, config.ErrInvalidNumberOfErasureEndpoints(nil).Msg(msg)
	}

	var setSize uint64
	// Custom set drive count allows to override automatic distribution.
	// only meant if you want to further optimize drive distribution.
	if setDriveCount > 0 {
		msg := fmt.Sprintf("Invalid set drive count. Acceptable values for %d number drives are %d", commonSize, setCounts)

        assertNotNull(paths);
        assertEquals(10, paths.size());
        assertEquals("test-extension-1.jar", paths.get(0).getFileName().toString());

        // JUnit has an "Automatic-Module-Name", so it appears on the module path.
        Map<PathType, List<Path>> dispatched = session.resolveDependencies(
                coord, PathScope.TEST_COMPILE, Arrays.asList(JavaPathType.CLASSES, JavaPathType.MODULES));

* **Convert data**: from the request to the required type.
* **Validate data**: coming from each request:
    * Generating **automatic errors** returned to the client when the data is invalid.
* **Document** the API using OpenAPI:
    * which is then used by the automatic interactive documentation user interfaces.

## Write the callback documentation code

This code won't be executed in your app, we only need it to *document* how that *external API* should look like.

But, you already know how to easily create automatic documentation for an API with **FastAPI**.