# Introduction to the Unity web request APIs

> Understand the main uses and architecture of Unity's web request APIs.

`UnityWebRequest` is Unity's HTTP/HTTPS networking API for communicating with web services, transferring files, and streaming data at runtime.

Common uses for the Unity web request system include:

* Downloading content at runtime, such as:

  * AssetBundles from remote servers, when using the regular [AssetBundle](/engine/6000.0/manual/assets-and-media/assets-managing-runtime/assetbundles-section.md) or [Addressables](https://docs.unity3d.com/Packages/com.unity.addressables@latest) systems.
  * Text/JSON for config, localization, and live tuning.
  * Images (as [Textures](/engine/6000.0/manual/materials-and-shaders/textures/textures-getting-started/textures.md)) and audio (as [AudioClips](/engine/6000.0/manual/audio/reference/class-audio-clip.md)) for dynamic content.
  * Build-time or runtime patching via remote manifests.

* Uploading data to servers, such as:

  * Player metrics.
  * Saved game state.
  * Error/exception logs and crash reports.
  * Custom telemetry and analytics.

* Integrating with content delivery networks, authentication and security, payment platforms, multiplayer services, diagnostics, and remote build pipelines.

* Implementing low-traffic, networked multiplayer and turn-based games, such as chess.

## Architecture

The Unity web request system consists of two layers:

* A [High-Level API](/engine/6000.0/manual/scripting/object-oriented-development/web-request/hlapi.md) (HLAPI) wraps the low-level API and provides a convenient interface for common operations.
* A [Low-Level API](/engine/6000.0/manual/scripting/object-oriented-development/web-request/llapi.md) (LLAPI) provides maximum flexibility for more advanced oeprations.

The system breaks down an HTTP transaction into the following operations:

* Sending data to the server.
* Receiving data from the server.
* HTTP flow control (for example, redirects and error handling).

Each of these operations are managed by a specific type of object, which you can use to customize and control aspects of the transaction:

* An [`UploadHandler`](/engine/6000.0/script-reference/unityengine/networking/uploadhandler.md) object handles transmission of data to the server.
* A [`DownloadHandler`](/engine/6000.0/script-reference/unityengine/networking/downloadhandler.md) object handles receipt, buffering, and postprocessing of data received from the server.
* A [`UnityWebRequest`](/engine/6000.0/script-reference/unityengine/networking/unitywebrequest.md) object manages the other two objects, and also handles HTTP flow control. This object is where custom headers and URLs are defined, and where error and redirect information is stored.


**Data sent from user code passes through an UploadHandler and then a UnityWebRequest before reaching the HTTP web server. Data received from the server passes through a UnityWebRequest and then a DownloadHandler before reaching user code.:**
![](/api/media?file=/engine/6000.0/media/images/UnityWebRequestArchitecture.png)

The following is a high level overview of a HTTP transaction:

* Create a [`UnityWebRequest`](/engine/6000.0/script-reference/unityengine/networking/unitywebrequest.md) object.

* Configure the `UnityWebRequest` object.

  * Set custom headers.
  * Set HTTP verb (such as `GET`, `POST`, `HEAD` - custom verbs are permitted on all platforms).
  * Set URL.

* (Optional) Create an upload handler and attach it to the web request.

  * Provide data to be uploaded.
  * Provide an HTTP form to be uploaded.

* (Optional) Create a download handler and attach it to the web request.

* Send the web request.
  * From a [coroutine](/engine/6000.0/manual/scripting/object-oriented-development/coroutines-section.md), you can `yield` the result of the [`UnityWebRequest.SendRequest`](ScriptRef:Networking.UnityWebRequest.SendRequest) call to wait for the request to complete.

* (Optional) Read received data from the download handler.

* (Optional) Read error information, HTTP status code, and response headers from the `UnityWebRequest` object.

For a detailed code example that illustrates these steps, refer to the API documentation for [`UploadHandlerRaw`](/engine/6000.0/script-reference/unityengine/networking/uploadhandlerraw.md).

## Additional resources

* [Web request high-level API reference](/engine/6000.0/manual/scripting/object-oriented-development/web-request/hlapi.md)
* [Web request low-level API reference](/engine/6000.0/manual/scripting/object-oriented-development/web-request/llapi.md)