To check whether it is possible to register a domain, WAPI interface offers command domain-check. 

CAUTION! Some domains, although they not exist, are not possible to register. Some names may be reserved, blocked or may otherwise be limited by their registration. It always depends on the particular registry, its rules, eventually ongoing conflicts.

For this command is applied limit max. 100 requests per hour. More in article  WAPI – limits.

• name – domain name(domain.tld)  – required

• 1000 – domain is available for registration
• 3201 – domain name is already used
• 3204 – domain is quarantined
• 3205 – domain is reserved
• 3206 – domain name is blocked

This command does not return any data  except the return value

XML request:

<request>
 <user>tester</user>
 <auth>e347aa51858cf6b6c017ae5d060fefca1b9dba38</auth>
 <command>domain-check</command>
 <clTRID>35c7</clTRID>
 <data>
  <name>example.cz</name>
 </data>
</request>

XML response:

<response>
 <code>1000</code>
 <result>OK</result>
 <timestamp>1286463108</timestamp>
 <clTRID>35c7</clTRID>
 <svTRID>1286463108.1704.23122</svTRID>
 <command>domain-check</command>
</response>

XML request:

<request>
 <user>tester</user>
 <auth>e347aa51858cf6b6c017ae5d060fefca1b9dba38</auth>
 <command>domain-check</command>
 <clTRID>25qV</clTRID>
 <data>
  <name>example2.cz</name>
 </data>
</request>

XML response:

<response>
 <code>3201</code>
 <result>Domain is already registered</result>
 <timestamp>1286463350</timestamp>
 <clTRID>25qV</clTRID>
 <svTRID>1286463350.2859.23122</svTRID>
 <command>domain-check</command>
</response>