* Based on Python type hints.
* Validation and documentation from these types.
* Dependency Injection system.

It doesn't use a data validation, serialization and documentation third-party library like Pydantic, it has its own. So, these data type definitions would not be reusable as easily.

# GraphQL

As **FastAPI** is based on the **ASGI** standard, it's very easy to integrate any **GraphQL** library also compatible with ASGI.

You can combine normal FastAPI *path operations* with GraphQL on the same application.

!!! tip
    **GraphQL** solves some very specific use cases.

    It has **advantages** and **disadvantages** when compared to common **web APIs**.

Thanks to <a href="https://www.starlette.io/testclient/" class="external-link" target="_blank">Starlette</a>, testing **FastAPI** applications is easy and enjoyable.

It is based on <a href="https://www.python-httpx.org" class="external-link" target="_blank">HTTPX</a>, which in turn is designed based on Requests, so it's very familiar and intuitive.

# 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

## Read the Tutorial first

The next sections assume you already read the main [Tutorial - User Guide: Security](../../tutorial/security/index.md){.internal-link target=_blank}.

    * But it provides you the tools to build simple web applications, with routing based on paths, etc.
    * If you are comparing Starlette, compare it against Sanic, Flask, Django, etc. Web frameworks (or microframeworks).
* **FastAPI**:

And then you also read how to handle [CORS with the `CORSMiddleware`](../tutorial/cors.md){.internal-link target=_blank}.

In this section we'll see how to use other middlewares.

## Adding ASGI middlewares

As **FastAPI** is based on Starlette and implements the <abbr title="Asynchronous Server Gateway Interface">ASGI</abbr> specification, you can use any ASGI middleware.

    The new docs will include Pydantic v2 and will use <a href="https://sqlmodel.tiangolo.com/" class="external-link" target="_blank">SQLModel</a> (which is also based on SQLAlchemy) once it is updated to use Pydantic v2 as well.

You can use the same dependency overrides from [Testing Dependencies with Overrides](testing-dependencies.md){.internal-link target=_blank} to alter a database for testing.

# Get Current User

In the previous chapter the security system (which is based on the dependency injection system) was giving the *path operation function* a `token` as a `str`:

=== "Python 3.9+"

    ```Python hl_lines="12"
    {!> ../../../docs_src/security/tutorial001_an_py39.py!}
    ```

=== "Python 3.8+"

    ```Python hl_lines="11"
    {!> ../../../docs_src/security/tutorial001_an.py!}
    ```

=== "Python 3.8+ non-Annotated"

    Again, just with that same Python type declaration, **FastAPI** gives you automatic, interactive documentation (integrating Swagger UI).

    Notice that the path parameter is declared to be an integer.

## Standards-based benefits, alternative documentation