Checking a website available or not in other terms - website active or not. We can check this with WHOIS.
If the WHOIS is giving result that website/domain is already registered, but website is not available, check A (IP) record associated with that. There is no A record means, the domain owner not yet setup Hosting and Website for his domain.
If the WHOIS is giving result - all the details like NS Records, A Records, but website not available means, there is some issue with website.
But what is WHOIS?
WHOIS (pronounced "who is") is a protocol that allows you to query a database to find out information about a domain name, such as the owner, contact details, and registration and expiration dates. WHOIS information is publicly available and can be accessed through a WHOIS lookup tool, which allows you to enter a domain name and view the WHOIS record for that domain.
The WHOIS database is maintained by the Internet Corporation for Assigned Names and Numbers (ICANN), which is the organization that coordinates the assignment of unique identifiers on the Internet, including domain names and IP addresses. ICANN requires that all registered domain names have accurate and up-to-date WHOIS information. WHOIS information can be useful for a variety of purposes, such as verifying the ownership of a domain name, checking the availability of a domain name, or contacting the owner of a domain name.
However, it is important to note that WHOIS information is publicly accessible and can be viewed by anyone. As a result, some people may choose to use privacy protection services to keep their personal information private in the WHOIS database.
Qatar's best WHOIS details for (Qatari Domain)on a single glace available here.