Namecoin records are in the form of key and value pairs. A name is a lowercase string of the form d/examplename whereas a value is a case-sensitive, UTF-8 encoded JSON object with a maximum of 520 bytes. The name should be RFC1035 (https://tools.ietf.org/html/rfc1035)-compliant.

A general Namecoin name can be an arbitrary binary string up to 255 bytes long with, 1024-bits of associated identifying information. A record on a Namecoin chain is only valid for around 200 days or 36,000 blocks after which it needs to be renewed. Namecoin also introduced .bit top-level domains that can be registered using Namecoin and can be browsed using specialized Namecoin-enabled resolvers. Namecoin wallet software as shown in the following screenshot can be used to register .bit domain names.

The name is entered and, after the Submit button is pressed, it will ask for configuration information such as DNS, IP, or identity:

As shown in the following screenshot, masteringblockchain will register as masteringblockchain.bit on the Namecoin blockchain: