BloggerでOGP(Open Graph Protocol)とかTwitter Cardとか

公式のvalidator
https://cards-dev.twitter.com/validator

たぶんこんな感じ。

<meta content='summary' name='twitter:card'/>
<meta expr:content='data:blog.canonicalUrl' name='twitter:url'/>
<meta expr:content='data:blog.homepageUrl' name='twitter:domain'/>
<meta expr:content='data:blog.canonicalUrl' property='og:url'/>
<b:if cond='data:blog.pageType == &quot;item&quot;'>
    <meta expr:content='data:blog.title + &quot; | &quot; + data:blog.pageName' name='twitter:title'/>
    <meta expr:content='data:blog.title + &quot; | &quot; + data:blog.pageName' property='og:title'/>
<b:else/>
    <meta expr:content='data:blog.title' name='twitter:title'/>
    <meta expr:content='data:blog.title' property='og:title'/>
</b:if>
<b:if cond='data:blog.metaDescription'>
    <meta expr:content='data:blog.metaDescription' name='twitter:description'/>
    <meta expr:content='data:blog.metaDescription' property='og:description'/>
</b:if>
<meta expr:content='&quot;http://blogger-entry-image.appspot.com/?s=s900&amp;u=&quot; + data:blog.url' name='twitter:image'/>
<meta expr:content='&quot;http://blogger-entry-image.appspot.com/?s=s900&amp;u=&quot; + data:blog.url' property='og:image'/>