Meta tags

<meta charset='utf-8'>

<!-- title -->
<title>···</title>
<meta property='og:title'  content='···'>
<meta name='twitter:title' content='···'>

<!-- url -->
<link rel='canonical'       href='http://···'>
<meta property='og:url'  content='http://···'>
<meta name='twitter:url' content='http://···'>

<!-- description -->
<meta name='description'         content='···'>
<meta property='og:description'  content='···'>
<meta name='twitter:description' content='···'>

<!-- image -->
<meta property="og:image"  content="http://···">
<meta name="twitter:image" content="http://···">

<!-- ua -->
<meta http-equiv='X-UA-Compatible' content='IE=edge,chrome=1'>

<!-- viewport -->
<meta name='viewport' content='width=device-width'>
<meta name='viewport' content='width=1024'>

More opengraph

<meta property='og:site_name' content='···'>
<meta property='og:type' content='website'>

<meta property='fb:app_id' content='···'>
<meta property='fb:admins' content='UID1,UID2'>
<!-- ···unless there's app_id -->

<meta property='og:audio' content='http://···/theme.mp3'>
<meta property='og:video' content='http://···/trailer.swf'>

See: OpenGraph protocol (developers.facebook.com)

Opengraph for articles

Apple-only

<meta name='format-detection' content='telephone=no'>

Progressive web apps

Add to homescreen

<meta name='mobile-web-app-capable' content='yes'>
<meta name='apple-mobile-web-app-capable' content='yes'>

<meta name='apple-mobile-web-app-status-bar-style' content='black'>
<!-- black | black-translucent | default -->

Theme color

<meta name='theme-color' content='#ff00ff'>

Android-only. See: Theme color

Manifest

<link rel='manifest' href='/manifest.json'>

Android-only. See: Manifest

Icons

<!-- Minimal -->
<link rel='icon' type='image/png' href='[email protected]'>
<link rel='icon' sizes='192x192' href='[email protected]'>
<link rel='apple-touch-icon' href='[email protected]'>
<meta name='msapplication-square310x310logo' content='[email protected]'>

<!-- Apple -->
<link rel='apple-touch-icon' href='touch-icon-iphone.png'>
<link rel='apple-touch-icon' sizes='76x76' href='touch-icon-ipad.png'>
<link rel='apple-touch-icon' sizes='120x120' href='touch-icon-iphone-retina.png'>
<link rel='apple-touch-icon' sizes='152x152' href='touch-icon-ipad-retina.png'>

<!-- Microsoft -->
<meta name='msapplication-square70x70logo' content='icon_smalltile.png'>
<meta name='msapplication-square150x150logo' content='icon_mediumtile.png'>
<meta name='msapplication-wide310x150logo' content='icon_widetile.png'>

Chrome on Android recommends 192x192. See: Icons

Reference