Fetch Standard
Every fetch() call and XHR request is governed by this spec. It also defines CORS behavior in detail.
What It Defines
Defines the browser Fetch API and the full request/response model used by browsers. Specifies the CORS protocol, origin checks, credential inclusion, and how fetch() maps to HTTP.
Canonical (Normative)
Convenient (Practical)
Maintains the living standards for the web platform: HTML, DOM, Fetch, URL, Streams, and more. These are continuously updated living documents, not versioned snapshots.
Related Specs
Every browser-side API call to a different origin hits CORS. Misconfigured CORS is a top source of dev frustration and security holes.
The spec behind every HTML page, form, and browser API. The canonical reference for how browsers actually parse and process HTML.
This is the core contract of every web API, browser request, and server response. You can't design or debug HTTP without knowing this.
Streams are how modern browsers handle large data: fetch response bodies, file reads, compression, and encoding are all stream-based. Understanding backpressure and piping is essential for efficient data processing.