If Cloudflare's API isn't for general domain availability checks, what alternative APIs are commonly used for this purpose?

For checking the general availability of domain names for new registration, you should look to APIs provided by domain registrars or dedicated domain data services. Popular options include APIs from registrars like Namecheap, GoDaddy, Gandi, or specialized providers such as WhoisXMLAPI or Domainr. These services offer robust endpoints to query WHOIS data or their own domain databases to determine if a domain is registered or available for purchase.