Guide · 3 min read ·
How link previews work and how to fix a bad one
When you paste a link into a chat, a post or a message, the app often turns it into a card with an image, a title and a short description. That card decides whether people click. If yours shows a blank grey box or a random logo, you are losing attention for free. This guide explains where those cards come from and how to get them right.
Where the preview comes from
The app does not guess. It fetches your page and reads a few tags from the head of the HTML. The standard is called Open Graph, created for Facebook and now used by LinkedIn, Slack, Discord, WhatsApp and many others. The main tags are og:title, og:description and og:image. If they are missing, apps fall back to the page title and whatever they can scrape, which is often poor.
X reads Open Graph too, but also has its own twitter:card tag that selects the style of card. With the value summary_large_image you get a big image above the title. Without it you get a small square thumbnail.
The image does most of the work
A preview with a good image gets noticed in a crowded feed, while a text only card disappears. The most reliable size is about 1200 by 630 pixels, which suits both the wide Facebook and LinkedIn cards and the large X card. Keep important words and logos near the middle, because some apps crop the edges, and keep the file reasonably small so it loads before the app gives up.
Always use a full address for the image, starting with https. A relative path such as a folder name may work in a browser but fail when another service reads your page.
Common reasons a preview looks wrong
Most bad previews come from a short list of causes.
- The tags are missing, so the app guesses and picks the wrong image or none.
- The tags are added by JavaScript after the page loads, and the crawler never sees them.
- The image is hosted somewhere that blocks other sites, or needs a login.
- The page redirects through several addresses, and the final one lacks the tags.
- The platform cached an old version and keeps showing it.
Why changing the tags does not change the card
Platforms store previews so they do not re-fetch the same page thousands of times. After you fix your tags, the old card can keep appearing for days. Each major platform has its own debugger or post inspector that lets you force a refresh. This checker always reads the live page, so it shows you the truth first, and you can then refresh each platform.
How to use this checker
Paste the address of the page you plan to share, whether that is your homepage, a launch post or a listing. The tool shows approximate previews for Facebook and LinkedIn style cards and for X, then lists each tag it found. Anything marked missing in red is worth fixing before you share. The previews are close to what people will see, but each platform styles its cards slightly differently, so treat them as a guide.
A quick pre launch routine
Run through these steps before you post your link anywhere important.
- Check the card for your homepage and for the exact link you are about to share.
- Make sure the title says what the page is, not just your company name.
- Use a distinct image for key pages, rather than the same logo everywhere.
- Add twitter:card with the value summary_large_image.
- Refresh the cached preview on each platform after any change.
Do the rest of your page too
A good card is one part of a good page. The launch page grader checks the search basics as well as the sharing tags, and your CircleSaaS listing gets a share image of its own automatically when you claim a tile. Put your best link where people will actually see it, and make sure it looks as good as the product behind it.