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Uniform Resource Identifiers (URI) are used to identify "resources" on the web. URIs are commonly used as targets of HTTP requests, in which case the URI represents a location for a resource, such as a document, a photo, binary data. The most common type of URI is a Uniform Resource Locator (URL), which is known as the web address.
URIs can be used to trigger behaviors other than fetching a resource, including opening an email client, sending
text messages, or executing JavaScript, when used in other places such as the href of an HTML <a> link.
The URI reference provides details about the components that make up a URI.
The first part of the URI, before the : character, which indicates the protocol the browser must use to fetch the resource.
The section that comes after the scheme and before the path. It may have up to three parts: user information, host, and port.
The section after the authority. Contains data, usually organized in hierarchical form, to identify a resource within the scope of the URI's scheme and authority.
The section after the path. Contains non-hierarchical data to identify a resource within the scope of the URI's scheme and naming authority along with data in the path component.
An optional part at the end of a URI starting with a # character. It is used to identify a specific part of the resource, such as a section of a document or a position in a video.
The URI guides help you work with URIs on the web.
Guidance on when sites should use a www. prefix in URLs (www.example.com vs example.com).
This page was last modified on Jun 22, 2026 by MDN contributors.
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