A share image is not a poster. It is read at a few hundred pixels wide, inside a scrolling feed, next to twenty other things competing for the same half second. Almost every rule below is a consequence of those three conditions.
None of them is about taste. A card can be beautiful in the editor and invisible in a feed, because the feed is a harder place to be read than a page. Design for where it lands, not for where you make it.
Write the headline first
The picture is the frame. The headline is the product. If you cannot say what the link is about in six to ten words, no amount of gradient will rescue the card.
Write it as a sentence a person would say out loud. "Ship faster with better previews" beats "Introducing our new preview pipeline v2". Lead with a verb or a number where you can, because both survive being skimmed. A vague headline on a beautiful card still loses to a plain headline that says what the reader gets.
If the card and the page title fight each other, the card wins, because it is what people see first. Make them agree.
Size type for the thumbnail
The most common mistake is type that looks generous at full size and turns to grey mush at unfurl size. A safe floor: your headline should be at least 1/12th of the canvas height. On a 1200 x 630 card that is roughly 52px, and bigger is usually better.
Shrink the card to 400px wide and look at it. If you have to lean in, the type is too small. Weight matters as much as size here: a thin weight that reads cleanly at full size can disappear once a platform downscales it, so prefer a medium or a semibold for anything that has to be read at a glance.
One idea per card
A headline, one supporting line, and a mark. That is the whole budget. Everything else you want to add is competing with the headline for the same half second.
Supporting text is optional. Most of the best cards do not have any. If you find yourself adding a second sentence to explain the first, the first sentence is the one to fix.
Contrast before colour
Aim for a contrast ratio of at least 4.5:1 between the headline and whatever sits behind it. Feeds render cards in both light and dark surroundings, at low brightness, on bad screens.
Colour is the part people spend the most time on and the part that matters least at thumbnail size. A high-contrast card in two colours reads; a low-contrast card in a carefully chosen ten-colour palette does not. Decide the contrast first, then spend whatever attention is left on the palette.
Where a photograph is behind the text, do not fight it. Put a solid or gradient scrim between them. A partly readable headline is worse than an obviously deliberate one.
Keep everything important in the middle
Platforms crop differently and none publish the exact rectangle they keep. The middle 87% survives everywhere, which on a 1200 x 630 canvas is about 1040 x 546.
Corners are the worst place on the card. They get cropped first, and rounded unfurls cut them again. Treat the outer band as bleed for decoration only, and keep the headline, the logo and anything that has to be read well inside the safe rectangle.
Give it a shape, not just a stack
Left-align the headline and let it sit on a consistent margin, or centre it and mean it. What reads as amateur is text that is almost aligned: a headline nudged off a margin the logo respects, or a supporting line that starts under a different edge than the line above it.
Pick one vertical rhythm and hold every element to it. Alignment is invisible when it is right and is the first thing that makes a card look thrown together when it is wrong.
Make the logo small
The instinct is to make the brand mark large. Resist it. At thumbnail size a big logo takes room from the only element that gets anyone to click, and readers already know who posted it: the account name is directly above the card.
A mark at 5 to 8% of the canvas height is plenty.
Be consistent enough to be recognised
Cards work hardest when someone has seen three of yours before. Fix the things that make a card recognisable and vary only the content:
- One typeface, or two at most.
- One accent colour.
- One layout family per content type. Blog posts share a layout, releases share another.
Consistency here is worth more than novelty. A feed is exactly the place where a familiar shape gets noticed.
Give the card a subject, not a texture
An abstract gradient says nothing. A screenshot of the thing, a number, a quote, or a single object all say something before the headline is read.
If the post is about a result, put the number on the card. If it is about a feature, show the feature. A product screenshot, even a small one in a corner, tells a reader what they are about to open in a way no background can. Decorative backgrounds are the fallback, not the plan, and they are the right call only when the subject genuinely is the words.
Check it in the dark
Half your readers are in dark mode, and a card designed on a white background can glow in a dark feed. Look at both. A near-white card is not wrong, but it should be a decision rather than an accident.
The reverse trap is a dark card that vanishes into a dark feed with no edge. If your background is close to the feed's own, add a hairline border or a subtle inner shadow so the card reads as an object rather than bleeding into the timeline.
The two minute review
Before you ship a card, check:
- Readable at 400px wide.
- Headline under ten words.
- Contrast at least 4.5:1.
- Nothing important within 7% of any edge.
- Everything aligned to one grid.
- Logo small.
- Recognisably yours.
- Checked against both a light and a dark background.