Key Takeaways
- Unfurling turns a link into a preview card built from the page's Open Graph tags.
- Set og:title, og:description and og:image on your pages so previews look right.
- Bots can switch previews off: Telegram link_preview_options, WhatsApp preview_url.
- Slack apps can create custom unfurls for their own domains.
What Is URL Unfurling?
URL unfurling is what happens when you paste a link into a chat and it expands into a card with the page's title, a short description and an image. The chat app fetches the page and reads its Open Graph tags (og:title, og:description, og:image), falling back to the HTML title and other metadata.
Link Previews on Each Platform
| Platform | How previews work | Control for bots |
|---|---|---|
| Slack | Unfurls links using page metadata | Apps can listen for link_shared and post a custom unfurl for their own domains |
| Discord | Shows an embed from Open Graph tags | Wrapping a link in angle brackets suppresses it; bots can send their own embeds |
| Telegram | Link preview under the message | link_preview_options in sendMessage, including disabling it |
| Preview card when enabled | The Cloud API's preview_url flag on text messages |
To design how your own message cards look instead, the Discord embed builder builds embeds visually.
Making Your Links Unfurl Well
- Give every page a unique
og:title,og:descriptionand a 1200x630og:image. - Keep the server fast and publicly reachable: unfurlers give up quickly.
- Turn previews off for bot messages that contain many links, so the chat is not flooded with cards.
- Add UTM parameters if you want to measure clicks from shared links - the UTM builder creates them.
Frequently Asked Questions
What does unfurl mean in Slack?
In Slack, to unfurl a link is to expand it into a preview showing the page title, description and image. Slack does this automatically for most public pages, and apps can provide richer custom unfurls for links to their own service by listening for the link_shared event.
Why is my link preview not showing?
Usually the page lacks Open Graph tags, the image is too small or blocked, the page is slow or behind a login, or the chat app cached an old version. Add og:title, og:description and og:image, make sure the page is public and fast, then share the link again.
How do I disable link previews in a Telegram bot?
Pass link_preview_options with is_disabled set to true in sendMessage. The same object lets you choose which URL to preview, show it above the text, or make the image smaller or larger, so you can keep one preview and suppress the rest.
Do WhatsApp business messages show link previews?
They can. In the WhatsApp Cloud API a text message has a preview_url option; when it is true and the message contains a link, WhatsApp shows a preview card. Leave it off for messages where a card would distract from the text.
What are Open Graph tags?
Open Graph tags are meta tags in a web page's head, such as og:title, og:description and og:image, that tell social networks and chat apps how to present the page when it is shared. They are the main source of the information shown in a link preview.
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