Browser - Fetching Resources (Request/Response)


Fetching is a web term that means to get a resource.

User agents can implement a variety of transfer protocols to fetch resources such as:

When the browser is rendering an HTML page, it encounters HTML elements that are executing fetching command (such as img that fetch an image). More … see HTML - Fetch Elements

Processing Model

When a user agent is to fetch a resource or URL:

  • optionally from an origin,
  • optionally using a specific referrer source as an override referrer source,
  • and optionally with any of a synchronous flag, a manual redirect flag, a force same-origin flag, and a block cookies flag,

it must follow this processing model.


A web site (HTML, Javascript or CSS) can fetch two types of resources from a server:


A web site (HTML, Javascript or CSS) is able to receive data resources (such as HTML, XML, or JSON documents) from:


Media resources such as images, JavaScript, CSS, or fonts can be included from any origin, even without permissive CORS headers.

Cross-Origin Read Blocking (CORB) prevents the fetch of a cross-origin data resource.






The origin request header indicates where a fetch originates from.


Documentation / Reference

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