* data serialization
* data documentation, etc.

This works the same way as with Pydantic models. And it is actually achieved in the same way underneath, using Pydantic.

!!! info
    Keep in mind that dataclasses can't do everything Pydantic models can do.

    So, you might still need to use Pydantic models.

    But if you have a bunch of dataclasses laying around, this is a nice trick to use them to power a web API using FastAPI. 🤓

        return param


class SecurityScopes:
    """
    This is a special class that you can define in a parameter in a dependency to
    obtain the OAuth2 scopes required by all the dependencies in the same chain.

    This way, multiple dependencies can have different scopes, even when used in the
    same *path operation*. And with this, you can access all the scopes required in
    all those dependencies in a single place.

        "optional-dependencies", {}
    )
    # Get custom optional dependencies name to always include in this (non-slim) package
    include_optional_dependencies: List[str] = config.get(
        "include-optional-dependencies", []
    )
    # Override main [project] configs with custom configs for this package
    for key, value in project_config.items():
        metadata[key] = value

    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {},

    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/": {
                "get": {
                    "responses": {
                        "200": {
                            "description": "Successful Response",

    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/teleport": {
                "get": {
                    "summary": "Get Teleport",
                    "operationId": "get_teleport_teleport_get",
                    "responses": {

If you generate a client for a FastAPI app using tags, it will normally also separate the client code based on the tags.

This way you will be able to have things ordered and grouped correctly for the client code:

<img src="/img/tutorial/generate-clients/image06.png">

In this case you have:

* `ItemsService`
* `UsersService`

### Client Method Names

    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/keyword-weights/": {
                "get": {
                    "responses": {
                        "200": {
                            "description": "Successful Response",

    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/items/": {
                "get": {
                    "responses": {
                        "200": {
                            "description": "Successful Response",

    - **name**: each item must have a name
    - **description**: a long description
    - **price**: required
    - **tax**: if the item doesn't have tax, you can omit this
    - **tags**: a set of unique tag strings for this item
    """