URL (Uniform Resource Locator)

Table of contents

Resources

www serves as the hostname. Domains without www are called naked domains or root domain or apex domain.

Choose one as the default (canonical). I use non-www as the default.
Namecheap can handle redirect of www to non-www. Alternatively, use HTTP 301 redirect.
In case you are serving both www and non-www domains with the same content, use <link rel="canonical" href="" /> to tell search engine the canonical domain. The search engine will treat both the domains as different, and penalize for duplicate content/spam and lower the page rank.
Do not use CNAME for the redirect. According to DNS specification, any domain that has a CNAME record set cannot have other DNS records associated with it. Instead use the A record to point to a server and from the server do HTTP 301 redirect.
It is more important to mantain consistency than deciding which url to use.

Benefits of www

At high traffic volumes (millions of daily users) www makes more sense.
Easier to manage DNS settings when using www.
Handling cookies is easier. A cookie set on example.com would apply to all subdomains as well.
CNAME record cannot be added to root domain. CDNs rely on CNAME records and using a non-www domain makes it harder to redirect traffic when servers experience issues. www.example.com can be redirected to mycdn.provider.net at the CDN level and mycdn.provider.net target can be changed whenever traffic needs to be rerouted.

https://www.example.com:80/path/to/file.html?key1=value1&key2=value2#SomewhereInTheDocument

Scheme http - Specify the protocol that the browser must use to request the resource.
Authority www.example.com:80 - Separated from the schema using ://. Includes both the domain www.example.com and the port 443 (ommitted if using standard ports 80 for HTTP and 443 for HTTPS).
Path to resource /path/to/file.html - Path to the resource on the web server. It can be an actual file or an abstraction handled by web servers without the presence of an actual file.
Parameters ?key1=value1&key2=value2 - The GET parameters.
Anchor #SomewhereInTheDocument - Location inside the resource itself.

For this absolute URL https://developer.mozilla.org/en-US/docs/Learn_web_development

Scheme-relative URL //developer.mozilla.org/en-US/docs/Learn_web_development - The browser will use the same protocol as the one used to load the document hosting that URL.
Domain-relative URL /en-US/docs/Learn_web_development - The protocol and domain name will be used from the host URL.
Sub-resource HowTo/Web_mechanics/What_is_a_URL - Browser will use path relative to en-US/docs/Learn_web_development. So the final URL becomes https://developer.mozilla.org/en-US/docs/Learn_web_development/HowTo/Web_mechanics/What_is_a_URL. We can use .. to move up a directory.
Anchor-only #semantic_urls - To link to different parts of the current document, as the browser will use the entire URL.

https://username:password@www.example.com:80

To immediately sign in to a website and bypass the username/password dialog box.
Deprecated in modern browsers. And the username/password info is stripped from the request before it is sent.

Keep it short and memorable, in case someone has to manually write down the URL in the browser.
Only use lowercase, as it removes the ambiguity, and also the official URL spec says to use lowercase.
Use readable slug instead of ID. A readable slug makes it easier to glean the content of the page by just looking at the URL.
Do not use spaces. Spaces also make it harder to identify the end of the URL.
Use hyphens instead of underscore, use kebab case. Also, when links are underlined on a page, the underscores get hard to see.
Use period only for domains and indicating file extensions.
If possible avoid using www in the URL.
Do not have .html in the URL, as it adds unncessary length.
Avoid trailing slash where it does not make sense. example.com/posts/ makes sense, since there is further content within posts/. But example.com/posts/post-title/ is bad.
URL’s structure should work as breadcrumb. And the user should be able to make their way back along the path without error at any stage.
Avoid date paths if you can example.com/posts/2025/02/24/post-title. It makes sense on news sites where there are multiple items releasing daily. Also, the date adds extra length to the url.