How each service shows links today

Checked on 5 October 2026 (Threads verified on 6 October on the web composer). Few items have official documentation; most are published observations. Services change without notice.

Settings that work everywhere

og:title, og:description, og:image and og:url. LINE reads only the first three.
A 1200×630 JPEG or PNG. Accepted formats and sizes differ by service (below).
twitter:card set to summary_large_image gives a large image card on X, Slack and Discord.
og:image:width and og:image:height make Facebook and Discord show the right size on the first share.

X

summary_large_image gives a 2:1 large image; summary or no twitter:card gives a small square thumbnail.
The large image card shows no description. The title is overlaid on the image and the domain appears below it (since January 2024).
Images under 5MB and at least 300×157. SVG is not shown. Animated GIFs stop on the first frame.
There is no official validator. Paste the URL in the compose box to check.

Facebook

Images 600×315 or larger give a large card; 200×200 up to 600×315 a small square thumbnail; under 200×200 or over 8MB, no image.
Without og:image:width and og:image:height, the first share may show an empty image frame.
The description shows up to about 155 characters on desktop and may not show on mobile.
The domain appears in capitals above the title.
Images that are not 1.91:1 are cropped from the centre.

Organic posts show a small thumbnail on the left with the title and domain on the right (since 2024). Large image cards are for sponsored posts only.
Images 1200×627 or larger recommended, up to 5MB, JPG, PNG or GIF. Under 401px wide is treated as a thumbnail.
Several observations report that the description does not show in the feed.
twitter:* tags are not read.

LINE

Reads only og:title, og:description and og:image. og:site_name and og:url are not used.
A landscape thumbnail of about 1.78:1; a 1200×630 image loses a little on the sides.
Image size and format requirements are not published.

Slack

summary_large_image gives a large image (scaled to about 360px wide); summary gives a small square thumbnail on the right.
og:site_name appears above the title. The description is shown.
Only the first 32KB of the page is read. Tags after that point are not seen.
No unfurl when the same link was posted in the same conversation within the last hour, or when a message has five or more links.

Discord

The default is a small thumbnail of about 80×80 on the right. summary_large_image, a landscape image wider than 400px, or og:image:width/height gives a large image.
Large images are scaled to about 400px wide and at most about 300px tall, without cropping.
<meta name="theme-color"> sets the colour of the left bar.
The description is shown (up to about 350 characters). The title is cut at about 256.
http:// images are not loaded.

iMessage

The default is a bubble with the title, domain and a small icon. With og:image, an image card.
The description is not shown.
Images under 150px wide are ignored or shown as an icon. 900px or wider is the guideline.
The sender’s device fetches the page. JavaScript is not executed.

Threads

Verified on 6 October 2026 in the web composer. The feed rendering after posting is unverified.

Always a large image card. The frame is about 2:1 and other ratios are cropped from the centre.
Images under 200px in width or height give a text-only card.
No description. Favicon, domain and the title (up to 2 lines) are shown. og:site_name is not used.
WebP, AVIF and GIF (animated GIFs play) are shown. SVG and images over 8MB are not.
Transparent areas of a PNG show #FAFAFA in light mode and #0A0A0A in dark mode.
Without og:image, the first image in the body is used. Without og:title, <title> is used.

Bluesky

Always a large image card, cropped from the centre into a 1200:630 frame.
Title and description are cut at 200 characters with .... The title has up to 3 lines, the description 2 with an image.
Images are converted to JPEG. Transparency is lost and has been observed to turn black.
Card content is written into the post, so fixing the page later does not change existing posts.
og:site_name is not used; a globe icon and the domain are shown.