URL redirection

URL redirection, also called URL forwarding, is a World Wide Web technique for making a web page available under more than one URL address. When a web browser attempts to open a URL that has been redirected, a page with a different URL is opened. Similarly, domain redirection or domain forwarding is when all pages in a URL domain are redirected to a different domain, as when wikipedia.com and wikipedia.net are automatically redirected to wikipedia.org.

URL redirection is done for various reasons:

for URL shortening;

to prevent broken links when web pages are moved;

to allow multiple domain names belonging to the same owner to refer to a single web site;

to guide navigation into and out of a website;

for privacy protection (such as redirecting YouTube and Twitter links to Invidious and Nitter respectively or to turn AMP links into normal links); and

for hostile purposes such as phishing attacks or malware distribution.

Purposes

There are several reasons to use URL redirection:

Forcing HTTPS

A website may potentially be accessible over both a secure HTTPS URI scheme and plain HTTP (an insecure URI beginning with "http://").

If a user types in a URI or clicks on a link that refers to the insecure variant, the browser will automatically redirect to the secure version in case the website is contained in the HSTS preload list shipped with the application or if the user had already visited the origin in the past.

Otherwise the website will be contacted over HTTP. A website operator may decide to serve such requests by redirecting the browser to the HTTPS variant instead and hopefully also priming HSTS for future accesses.

Similar domain names

A user might mistype a URL. Organizations often register these misspelled domains and redirect them to the intended location. This technique is often used to "reserve" other top-level domains (TLD) with the same name, or make it easier for a ".edu" or ".net" site to accommodate users who type ".com".

Moving pages to a new domain

Web pages may be redirected to a new domain for three reasons:

a site might desire, or need, to change its domain name;

an author might move their individual pages to a new domain;

two web sites might merge.