Uniform Resource Locators (URLs) are text strings that allow a resource such as a file or other object to be labelled based on its location on an internetwork and the primary method or protocol by which it may be accessed. URLs have become the most common type of Uniform Resource Identifier (URI) used for application layer addressing in TCP/IP because of their simplicity.

In this section I provide a detailed explanation of Uniform Resource Locators and how they are used. I begin with an overview of the general syntax used for standard URLs, sometimes called “absolute” URLs to distinguish them from relative URLs. I then provide a description of the URL schemes used for the most common applications and access methods, and the specific syntax used by each. I then discuss how relative URLs work and why they are important. Finally, I discuss some of the real world issues associated with using URLs; this includes problems related to long and complex URLs, as well as the intentional obfuscation “games” being played by some unscrupulous people.