Subdomains vs Subdirectories

How to choose when creating something for CMU

When structuring a website as large and diverse as cmu.edu, it’s important to understand the difference between subdomains and subdirectories—two common ways of organizing content online. While both serve to separate and categorize information, they function differently from a technical and SEO standpoint. Choosing the right structure can affect how users navigate the site, how content is managed across departments, and how search engines like Google understand and rank your pages. Learn about the key differences between subdomains and subdirectories, along with their respective impacts on search engine optimization, to help inform strategic decisions for what makes the most sense to your needs.

If someone at cmu.edu has sent you this page, it’s likely because you requested a subdomain, but best practices dictate that you should really use a subdirectory instead. 

What is a subdomain?

A subdomain is a separate section of a website that operates under the main domain but can function independently. Subdomains are mostly considered their own website in the eyes of search engines, and often do not carry the same weight as the root domain.

Format: subdomain.cmu.edu

Best for:

• Large, semi-independent entities like cs.cmu.edu
• Finite time periods
• Internal data (think student-run labs)

Pros:

• Good for autonomy — departments or research centers can run independently.
• Can isolate technical or security concerns.

Cons:

• Google often treats them as separate sites — SEO equity from cmu.edu may not transfer.
• Requires independent SEO efforts (keywords, backlinks, content updates).
• Can dilute brand authority if not well-integrated.

What is a subdirectory?

A subdirectory is a folder within the main website structure. Subdirectories (sometimes also referred to as subfolders) are basically folders within the root of a website, and carry the same weight and authority as the rest of www.cmu.edu. For net-new external-facing websites, subdirectories will provide the best and fastest SEO authority.

Format: cmu.edu/subdirectory

Best for:

• Content that’s part of the core CMU experience (admissions, events, news, etc.)
• SEO (in most cases)
• Most external audiences
• Anything part of the main site’s hierarchy

Pros:

• Benefit from the main site’s domain authority.
• Easier to manage internal linking and SEO strategies.
• Centralized analytics and performance tracking.

Cons:

• Difficult to set up non-CMU content management systems, such as WordPress or GitHub Pages.

What’s the Difference Between Subdomains and Subdirectories?

* Note: CMU-supported CMS platforms like Cascade and Drupal allow for some flexibility within subdirectories, but full separation may require a subdomain.

SEO Recommendations for Subdomains/Subdirectories

Or: Why Subdirectories Are Almost Always Better When Requesting a New Site on cmu.edu

The SEO best-practice recommendation is to use subdirectories in most instances. It is rare to see website requests for new CMU initiatives, departments, labs, or anything else that merit the use of new subdomains.

There are still a few instances where a subdomain would work better than a subdirectory. See examples below.

Other Considerations

Who’s the Audience?

• General public, prospective students, or media? Use a subdirectory
• Internal use, such as student labs, internal staff events, or information behind logins A subdomain may be better

Content Management System (CMS)

• Using Cascade or Drupal (CMU’s main systems)? Likely a subdirectory
• Using something else (such as WordPress or GitHub Pages)? Likely a subdomain

Branding Independence

• Will the site still look, feel, and read like a CMU site? Use a subdirectory
• Is it meant to look separate, with its own branding? Use a subdomain

Examples of Best Practice for Using Subdirectories vs. Subdomains

Example 1: A Campaign Website

Let’s say CMU is launching a new initiative called "Space!" to promote space-related research and events.

Best practice: Use a subdirectory (Example URL: www.cmu.edu/space)

Since this campaign is part of the university's core messaging and will be marketed under the CMU brand, placing it under the main domain helps it benefit from CMU’s domain authority and brand recognition.

Example 2: Student Life Resources

You’re launching a resource hub for student wellness services, events, and support initiatives under the Division of Student Affairs.

Best practice: Use a subdirectory

This content is primarily for current and prospective students, is relevant to the CMU community, and should carry the look and feel of the CMU brand.

Example 3: Independent Art Gallery

CMU received funding for a new art gallery. It has its own staff, a separate advisory board, and plans to publish independent content, host events, and use its own branding and CMS.

Best practice: Use a subdomain (example URL: ica.cmu.edu)

Because the center operates semi-independently and may serve academic or industry audiences without any input from CMU, a subdomain provides flexibility while still linking back to the university.

Example 4: School Magazine

Let’s say leadership within the Dietrich College wants to create a virtual magazine to send to alumni, highlighting the great work that current students and faculty are doing. The site will have added visual elements to make it stand out from regular site news articles and will be used for an internal audience only.

Best practice: Use a subdirectory (example URL: www.cmu.edu/dietrich/magazine

Even though visual elements may be different from the normal web experience, and the audience is entirely internal, because a magazine would be CMU-specific, best practice indicates it should be a subdirectory rather than a subdomain.

Example 5: New Web Application for a Student Project

Imagine a student just created a web application that turns typed text into code that looks like it came out of a cheesy movie where someone is hacking a mainframe in real time. It sits outside of the central CMU content management systems.

Best practice: Use a subdomain (example URL: www.andrew.cmu.edu/course/16-726-sp24)

If there’s something that requires entirely different hosting, CMS, or is an application-based platform, a subdomain will likely be the better choic.

Related Subdomain/Subdirectory Questions

What do we mean by domain authority?

Domain authority refers to the overall strength, trustworthiness, and credibility of a website in the eyes of search engines like Google. Authority comes from the longstanding value of a domain — in other words, how long a site has been around and how trustworthy its information is.

It’s not necessarily a ranking factor used directly by Google, but it’s a helpful concept in SEO to understand how likely a site is to rank well in search results.

What are third-level subdomains?

A third-level subdomain is simply a subdomain within another subdomain. It adds an extra layer to the domain structure, making it more specific.

When should you use third-level subdomains?

• Organizing content within a large subdomain (such as research groups within the CS department)
• Isolating web apps or services

My existing website space is on a subdomain already. Can I request it go back to a subdirectory?

You can request it, but the answer to whether the web team can actually do anything about it is probably a “no.” Once a site is set up, it is difficult internally to move from one experience to another.

Key Takeaways

• Use subdirectories for public-facing content that’s part of the CMU brand.
• Use subdomains only when technical or organizational independence is absolutely necessary — but ensure SEO consistency (title tags, structured data, mobile performance, etc.).