title: Purpose of package "Microsoft.EntityFrameworkCore.Design"
body: <p>All tutorials agree that <code>project.json</code> should include:</p>
  
  <pre class="lang-json prettyprint-override"><code>"Microsoft.EntityFrameworkCore.Design": 
  { 
      "type":"build", 
      "version":"1.0.0-preview2-final" 
  }
  </code></pre>
  
  <p>I have never included it, and have never had a problem.</p>
  
  <p>I only include</p>
  
  <pre><code>"Microsoft.EntityFrameworkCore"
  "Microsoft.EntityFrameworkCore.Sqlite"   (or Sqlserver)
  "Microsoft.EntityFrameworkCore.Tools"
  </code></pre>
  
  <p>What does this package do? Why can I exclude it without problems?</p>
  
  <hr>
  
  <p>UPDATE: see comments in accepted answer to figure out which package to import in which scenario.</p>