# URL Loading System Interact with URLs and communicate with servers using standard Internet protocols. ## Discussion The URL Loading System provides access to resources identified by URLs, using standard protocols like `https` or custom protocols you create. Loading is performed asynchronously, so your app can remain responsive and handle incoming data or errors as they arrive. You use a [`URLSession`](/documentation/Foundation/URLSession) instance to create one or more [`URLSessionTask`](/documentation/Foundation/URLSessionTask) instances, which can fetch and return data to your app, download files, or upload data and files to remote locations. To configure a session, you use a [`URLSessionConfiguration`](/documentation/Foundation/URLSessionConfiguration) object, which controls behavior like how to use caches and cookies, or whether to allow connections on a cellular network. You can use one session repeatedly to create tasks. For example, a web browser might have separate sessions for regular and private browsing use, where the private session doesn’t cache its data. [Figure 1](/documentation/foundation/url_loading_system#2927983) shows how two sessions with these configurations can then create multiple tasks.  Each session is associated with a delegate to receive periodic updates (or errors). The default delegate calls a completion handler block that you provide; if you choose to provide your own custom delegate, this block is not called. You can configure a session to run in the background, so that while the app is suspended, the system can download data on its behalf and wake up the app to deliver the results. ## Topics ### Essentials Configure and create sessions, then use them to create tasks that interact with URLs. [Fetching website data into memory](/documentation/Foundation/fetching-website-data-into-memory) Receive data directly into memory by creating a data task from a URL session. [Analyzing HTTP traffic with Instruments](/documentation/Foundation/analyzing-http-traffic-with-instruments) Measure HTTP-based network performance and usage of your apps. [`URLSession`](/documentation/Foundation/URLSession) An object that coordinates a group of related, network data transfer tasks. [`URLSessionTask`](/documentation/Foundation/URLSessionTask) A task, like downloading a specific resource, performed in a URL session. ### Requests and responses [`URLRequest`](/documentation/Foundation/URLRequest) A URL load request that is independent of protocol or URL scheme. [`NSURLRequest`](/documentation/Foundation/NSURLRequest) A URL load request that is independent of protocol or URL scheme. [`NSMutableURLRequest`](/documentation/Foundation/NSMutableURLRequest) A mutable URL load request that is independent of protocol or URL scheme. [`URLResponse`](/documentation/Foundation/URLResponse) The metadata associated with the response to a URL load request, independent of protocol and URL scheme. [`HTTPURLResponse`](/documentation/Foundation/HTTPURLResponse) The metadata associated with the response to an HTTP protocol URL load request. ### Uploading [Building a resumable upload server with SwiftNIO](/documentation/Foundation/building-a-resumable-upload-server-with-swiftnio) Support HTTP resumable upload protocol in SwiftNIO by translating resumable uploads to regular uploads. [Uploading data to a website](/documentation/Foundation/uploading-data-to-a-website) Post data from your app to servers. [Uploading streams of data](/documentation/Foundation/uploading-streams-of-data) Send a stream of data to a server. [Pausing and resuming uploads](/documentation/Foundation/pausing-and-resuming-uploads) Pause and resume an upload without starting over, even when the connection is interrupted. ### Downloading [Downloading files from websites](/documentation/Foundation/downloading-files-from-websites) Download files directly to the filesystem. [Pausing and resuming downloads](/documentation/Foundation/pausing-and-resuming-downloads) Allow the user to resume a download without starting over. [Downloading files in the background](/documentation/Foundation/downloading-files-in-the-background) Create tasks that download files while your app is inactive. ### Cache behavior [Accessing cached data](/documentation/Foundation/accessing-cached-data) Control how URL requests make use of previously cached data. [`CachedURLResponse`](/documentation/Foundation/CachedURLResponse) A cached response to a URL request. [`URLCache`](/documentation/Foundation/URLCache) An object that maps URL requests to cached response objects. ### Authentication and credentials [Handling an authentication challenge](/documentation/Foundation/handling-an-authentication-challenge) Respond appropriately when a server demands authentication for a URL request. [`URLAuthenticationChallenge`](/documentation/Foundation/URLAuthenticationChallenge) A challenge from a server requiring authentication from the client. [`URLCredential`](/documentation/Foundation/URLCredential) `A`n authentication credential consisting of information specific to the type of credential and the type of persistent storage to use, if any. [`URLCredentialStorage`](/documentation/Foundation/URLCredentialStorage) The manager of a shared credentials cache. [`URLProtectionSpace`](/documentation/Foundation/URLProtectionSpace) A server or an area on a server, commonly referred to as a realm, that requires authentication. ### Network activity attribution ### Cookies [`HTTPCookie`](/documentation/Foundation/HTTPCookie) A representation of an HTTP cookie. [`HTTPCookieStorage`](/documentation/Foundation/HTTPCookieStorage) A container that manages the storage of cookies. ### Errors [`URLError`](/documentation/Foundation/URLError) Error codes returned by URL loading APIs. [URL Loading System error info keys](/documentation/Foundation/url-loading-system-error-info-keys) Recognize these keys from the user info dictionary of error objects produced by URL Loading APIs. ### Legacy [Legacy URL Loading Systems](/documentation/Foundation/legacy-url-loading-systems) Migrate your code away from using these legacy objects. --- Copyright © 2026 Apple Inc. 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