URL redirection

Key takeaways

URL redirection belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect URL redirection to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of URL redirection from memory before moving on to harder problems.

Reference excerpt

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. With URL redirects, incoming links to an outdated URL can be sent to the correct location. These links might be from other sites that have not realized that there is a change or from bookmarks/favorites that users have saved in their browsers. The same applies to search engines. They often have the older/outdated domain names and links in their database and will send search users to these old URLs. By using a "moved permanently" redirect to the new URL, visitors will still end up at the correct page. Also, in the next search engine pass, the search engine should detect and use the newer URL.

Logging outgoing links The access logs of most web servers keep detailed information about where visitors came from and how they browsed the hosted site. They do not, however, log which links visitors left by. This is because the visitor's browser has no need to communicate with the original server when the visitor clicks on an outgoing link. This information can be captured in several ways. One way involves URL redirection. Instead of sending the visitor straight to the other site, links on the site can direct to a URL on the original website's domain that automatically redirects to the real target. This technique bears the downside of the delay caused by the additional request to the original website's server. As this added request will leave a trace in the server log, revealing exactly which link was followed, it can also be a privacy issue. The same technique is also used by some corporate websites to implement a statement that the subsequent content is at another site, and therefore not necessarily affiliated with the corporation. In such scenarios, displaying the warning causes an additional delay.

Short aliases for long URLs

Web applications often include lengthy descriptive attributes in their URLs which represent data hierarchies, command structures, transaction paths and session information. This practice results in a URL that is aesthetically unpleasant and difficult to remember, and which may not fit within the size limitations of microblogging sites. URL shortening services provide a solution to this problem by redirecting a user to a longer URL from a shorter one.

Meaningful, persistent aliases for long or changing URLs

Sometimes the URL of a page changes even though the content stays the same. Therefore, URL redirection can help users who have bookmarks. This is routinely done on Wikipedia whenever a page is renamed.

Post/Redirect/Get

Post/Redirect/Get (PRG) is a web development design pattern that prevents some duplicate form submissions if the user clicks the refresh button after submitting the form, creating a more intuitive interface for user agents (users).

Device targeting and geotargeting Redirects can be effectively used for targeting purposes like geotargeting. Device targeting has become increasingly important with the rise of mobile clients. There are two approaches to serve mobile users: Make the website responsive or redirect to a mobile website version. If a mobile website version is offered, users with mobile clients will be automatically forwarded to the corresponding mobile content. For device targeting, client-side redirects or non-cacheable server-side redirects are used. Geotargeting is the approach to offer localized content and automatically forward the user to a localized version of the requested URL. This is helpful for websites that target audience in more than one location and/or language. Usually server-side redirects are used for Geotargeting but client-side redirects might be an option as well, depending on requirements.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with URL redirection

Start with the simplest possible case. Write down what URL redirection claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to URL redirection before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about URL redirection ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of URL redirection

In research: URL redirection appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses URL redirection in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: URL redirection is common in secondary-school and first-year university syllabi. It links to neighbouring topics Black hat search engine optimization, Internet search, Internet terminology, so understanding it makes those chapters shorter.
In everyday life: Look for URL redirection outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study URL redirection in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what URL redirection means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain URL redirection out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is URL redirection in simple terms?

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.

Why does URL redirection matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study URL redirection?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on URL redirection.