URLs

URLs, or Uniform Resource Locators, are strings used to identify resources on the Internet and indicate how to access them. They encode the means of retrieving a resource, including the protocol to use and the location to reach. In practice, URLs enable software such as browsers and APIs to fetch, view, or manipulate resources without user guidance.

A typical URL has several parts. The scheme (or protocol) names the access method, for example http or https. The authority may include an optional user information segment, the host name, and an optional port. The path identifies the resource on the host, and may be followed by a query string that passes parameters and a fragment identifier that refers to a subpart of the resource. Example: https://www.example.com/path/to/resource?query=value#section. Absolute URLs contain the full set of parts; relative URLs omit the scheme and host and are resolved against a base URL.

Common schemes include http, https, ftp, mailto, file, and data. URLs are ubiquitous in web pages, APIs, and email, serving as both hyperlinks and addresses. They may include characters outside the allowed set through percent-encoding, such as encoding a space as %20.

Resolution and access typically involve resolving the host via DNS, establishing a connection, and transferring data according to the scheme. HTTPS URLs use TLS to encrypt the connection. URLs can be subject to redirection, normalization, and security considerations, such as avoiding sensitive data in query strings.

Relation to URIs: a URL is a type of URI that locates a resource; the broader concept is URI. The standardization of these concepts has evolved through early web specifications and RFCs, notably RFC 1738 and RFC 3986.