Tag priority

Slack checks metadata in this order:

1. oEmbed: if a <link> tag or HTTP Link header points to an oEmbed endpoint, Slack uses that first
2. Twitter Card and Open Graph tags: whichever appears first in the HTML wins when both define the same property

If you have an oEmbed endpoint, Slack prefers it over inline meta tags.

Open Graph tags

Slack reads these OG tags for unfurls:

Twitter Card tags

Slack reads Twitter Card tags interchangeably with OG tags. The twitter:card value controls image layout:

• summary_large_image: large image in the unfurl
• summary: small square thumbnail alongside the text

Extra metadata fields

Slack supports twitter:label1/twitter:data1 and twitter:label2/twitter:data2 tag pairs. These render as additional key-value fields in the unfurl, up to two pairs.

<meta name="twitter:label1" content="Reading time">
<meta name="twitter:data1" content="5 minutes">
<meta name="twitter:label2" content="Published">
<meta name="twitter:data2" content="Feb 15, 2026">

Useful for articles, products, recipes, and anywhere extra context helps.

oEmbed

Slack fully supports oEmbed discovery via <link> tags and HTTP Link headers. oEmbed responses can include embedded players and custom HTML for rich unfurls.

<link rel="alternate" type="application/json+oembed"
      href="https://example.com/oembed?url=https://example.com/page">

App-based unfurling

Slack apps can use the chat.unfurl API for fully custom unfurl content on specific domains. This overrides automatic tag-based unfurling and supports buttons and structured data.

Minimal setup

All you need for good Slack unfurls:

<meta property="og:title" content="Your Page Title">
<meta property="og:description" content="A brief description of the page.">
<meta property="og:image" content="https://example.com/image.jpg">
<meta property="og:site_name" content="Your Site">
<meta name="twitter:card" content="summary_large_image">