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>
  <parse title="API" displaytitle="API">
    <text xml:space="preserve">&lt;p&gt;&lt;a href=&quot;/wiki/index.php?title=%E3%83%97%E3%83%AD%E3%82%B8%E3%82%A7%E3%82%AF%E3%83%88:Sandbox&amp;amp;action=edit&amp;amp;redlink=1&quot; class=&quot;new&quot; title=&quot;プロジェクト:Sandbox (存在しないページ)&quot;&gt;プロジェクト:Sandbox&lt;/a&gt;
&lt;/p&gt;
&lt;!-- 
NewPP limit report
CPU time usage: 0.009 seconds
Real time usage: 0.010 seconds
Preprocessor visited node count: 2/1000000
Preprocessor generated node count: 12/1000000
Post‐expand include size: 31/2097152 bytes
Template argument size: 0/2097152 bytes
Highest expansion depth: 2/40
Expensive parser function count: 0/100
--&gt;
</text>
    <langlinks />
    <categories />
    <links>
      <pl ns="4" xml:space="preserve">プロジェクト:Sandbox</pl>
    </links>
    <templates>
      <tl ns="4" xml:space="preserve">プロジェクト:Sandbox</tl>
    </templates>
    <images />
    <externallinks />
    <sections />
    <iwlinks />
    <properties />
  </parse>
</api>