You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information. 
<?xml version="1.0"?>
<api>
  <query>
    <blocks>
      <block id="6" by="CVargas" timestamp="2017-08-03T13:59:03Z" expiry="2017-08-04T13:59:03Z" reason="Has sido bloqueado automáticamente porque tu dirección IP ha sido usada recientemente por «[[User:JColmenarez|JColmenarez]]».&#10;El motivo por el que se bloqueó a [[User:JColmenarez|JColmenarez]] es «»." automatic="" nocreate="" />
      <block id="5" user="JColmenarez" by="CVargas" timestamp="2017-08-03T13:59:03Z" expiry="infinity" reason="" nocreate="" autoblock="" />
      <block id="4" user="AAlvarez" by="CVargas" timestamp="2017-03-24T19:44:54Z" expiry="infinity" reason="" nocreate="" autoblock="" />
      <block id="3" user="JChahine" by="CVargas" timestamp="2017-03-24T19:44:36Z" expiry="infinity" reason="" nocreate="" autoblock="" />
      <block id="2" user="GGarzon" by="CVargas" timestamp="2017-03-24T19:44:16Z" expiry="infinity" reason="" nocreate="" autoblock="" />
      <block id="1" user="CParada" by="CVargas" timestamp="2017-03-24T19:43:37Z" expiry="infinity" reason="" nocreate="" autoblock="" />
    </blocks>
  </query>
</api>