Undernames, a unique feature in the AR.IO - Your gateway to the permaweb Network, offer an innovative approach to managing subdomains within the Arweave Name System (ArNS).

Here's a quick rundown of how they work:

• Subdomains: Undernames are essentially subdomains for a registered ArNS name. There’s only a slight difference in formatting: an underscore _ instead of the usual dot .

• Control: The owner of the primary ArNS name has exclusive rights to configure undernames. For instance, the owner of "ardrive" can create and manage "dapp_ardrive".

• Configuration: Undernames are set up in the ANT (Arweave Name Token) associated with the main name. ANT owners can define multiple undernames, each pointing to different Arweave Transaction IDs.

Key Features of Undernames

Undernames go beyond underscores. They have flexibility and parameters worth noting:

1. Default Allocation: Every registered ArNS name comes with 10 undernames at no extra cost. This allocation can be expanded as required through individual purchases.

2. Build Credibility: Similar to the DNS space, scammers may try to mimic existing ArNS names. For instance, the ArNS name "dapp-ardrive" looks like "dapp_ardrive", which is an undername uniquely tied to the owner of "ardrive". Watch the underscores in ArNS names to establish credibility.

3. Character Limit: The total character count for a string of undernames and separators must not exceed 63 characters. In other words, the entire combination of undername, underscore and ArNS name needs to be below this limit.

4. Versatility and Utility: Undernames enhance the flexibility and usefulness of owning an ArNS name, allowing for a wider range of applications and organizational structures.

Undernames add a layer of distinctiveness to the Arweave Name System, providing owners with greater control and customization.

Example of an Undername

Imagine you own an ArNS domain named example. This is your primary ArNS name. Now, you want to create subdomains for different purposes or services related to example. This is where undernames come into play.

1. Primary Domain: example

   • This is your registered ArNS domain.

2. Creating Undernames:

   • Let's say you want to create a subdomain for a blog related to example. You can configure an undername like blog_example.

   • For a separate service, like a photo gallery, you might create another undername such as gallery_example.

3. Usage:

   • These undernames (blog_example, gallery_example) are unique to your primary domain example.

   • They provide a way to organize and categorize different services or sections of your website, each potentially pointing to different Arweave Transaction IDs.

4. Distinctiveness:

   • It's important to note that undernames, due to their underscore usage (_), should not be confused with or mimic other ArNS domains. For example, blog-example would be a completely different domain, not associated with example.

5. Character Limit:

   • The total length of an undername, underscore and ArNS name cannot exceed 63 characters. But don’t stress: you still have room for super long undernames like antidisestablishmentarianism_example

In summary, an undername like blog_example under the primary domain example offers a structured and secure way to expand and categorize your online presence within the permaweb. This approach ensures domain integrity and easy management of multiple subdomains​​.

Chart: Understanding Undernames in AR.IO Network