What is a Url?

John Spacey, March 22, 2018

A URL, or Uniform Resource Locator , is an address for locating files and services on the internet. They are used by people, websites, mobile apps, services, software applications, systems, scripts and infrastructure to connect to internet resources.

URL Parts

URLs can be broken down into several component parts:

A scheme is the internet protocol to use to access the resource such as https for hypertext transfer protocol encrypted with SSL. Hostname is a human readable address that maps to an IP address that can be located by internet networking technologies. Path is the resource that is being requested.

Query

A query can be appended to a URL with a "?" character as follows.

This is a way to pass parameters to a service as a list of name-value pairs.

Fragment

A fragment can be appended to a URL with a "#" character as follows.

This is used to specify a section or part of a document.

URL Normalization

There are several rules that are used to clean up unsightly URLs by mapping them to a standard version. For example, uppercase letters in a host name are mapped to lower case letters and standard port numbers are removed.

Uppercase letters in the path aren't changed.

Clean URLs

As a general principle, URLs are typically designed to be human readable wherever possible. This means that URLs are guessable such that people could change them to look for information. For example, the following URL can be considered clean.

https://simplicable.com/new/url

This URL isn't particularly clean:

https://simplicable.com/PageLauncher?p=6AFE8AA494844F1

Another common principle related to URLs is that information security should never rely on a complex "unguessable" URL.

Relative URLs

A resource can link to itself using only the path of the URL. A query and fragment can also be specified. This is commonly done on mobile web pages to reduce the size of the page for the purposes of speed and bandwidth reduction. For example, a page on simplicable.com can link to this page with the URL: /new/url.

URL Shortners

A URL shortner is a service that provides permanent short URLs such as:

http://goo.gl/Z4Dzv3

This is popular for sharing long URLs on social media. The provider of the short URL may collect data as they redirect each request. In some cases, the provider may share this data with the person who created the short URL. This is a way to track how many people click on a link.

Hostname vs Domain Name

A domain name is an internet address that is owned by an organization or individual such as:

google.com

A hostname can be the same as a domain name or it can add additional strings at the front of the domain known as subdomains such as:

cloud.google.com

Each subdomain has a "." character after it. These can be added to many levels. However, it is a common principle to never add more than one subdomain.

URL vs URI

A URL is a type of URI, or Uniform Resource Identifier. In other words, URLs are based on a standard known as URI. This standard is used to address other things such as email addresses. The following is a summary of the URI standard:

scheme:[//[user[:password]@]host[:port]][/path][?query][#fragment]

Overview: Url
Type	Internet Networking Basics
Definition	An address for locating files and services on the internet.
Also Known As	Web Address
Invented By	Tim Berners-Lee
Related Concepts	Internet » Human Readable » Networking » Information Security »