Design OG Images That Look Sharp in Slack Channels
Slack is where your links get shared to coworkers, clients, and collaborators. The preview card that Slack generates from your OG tags is often the deciding factor in whether someone clicks through or keeps scrolling through their channel backlog.
How Slack's Unfurling Engine Works
Slack uses a process called unfurling to expand URLs into rich preview cards. When someone pastes a link, Slack's servers fetch the page, parse the OG tags, and render an inline card with the image, title, and description. Unlike client-side preview generation in WhatsApp, Slack does this server-side, which means your page needs to be accessible to Slack's crawler at the IP ranges they publish. Sites behind VPNs, staging environments with IP restrictions, or pages that require JavaScript rendering for OG tags will produce broken or empty unfurls. Slack caches unfurled data for approximately 30 minutes, so updates to your OG tags take effect relatively quickly compared to Facebook or LinkedIn.
Image Display in Slack's Compact and Full Views
Slack offers users the ability to collapse or expand link previews, and many power users keep their channels in a compact view to reduce visual noise. In compact view, your OG image is hidden entirely, and only the title and a snippet of the description are visible. In full view, the image appears below the text at a constrained width that varies based on the sidebar and thread panel state. This means your OG image is supplementary to the text content in Slack, not the primary attention-grabber. Design it to reinforce the title rather than carry the entire message. A clean visual that confirms what the title says is more effective than a standalone graphic that requires interpretation.
Enterprise Slack Environments and Link Restrictions
Many Slack workspaces in enterprise environments have link preview restrictions configured by workspace admins. Some organizations disable unfurling for external links entirely, while others restrict it to approved domains. If you are building a SaaS product and sharing documentation or marketing links in customer-facing Slack channels, your OG image might never be seen by some users. This does not mean you should skip OG optimization, but it does mean your og:title and og:description need to carry the full message on their own. Think of the OG image as an enhancement in Slack, not a requirement. The title alone should be compelling enough to earn a click.
Thread Previews and Slack Connect Channels
Slack Connect channels, where different organizations share a workspace, present a unique context for link previews. Links shared in these channels are seen by external partners, clients, or vendors, which raises the stakes for how professional your preview looks. In threads, link previews are rendered at a slightly smaller size, and the image becomes even more secondary to the text. For links that will be shared in professional Slack Connect contexts, treat your OG image the way you would treat a business card. Clean, branded, and minimal. Skip the playful illustrations and clever copy that might work in an internal team channel. Let your brand identity speak through consistent colors and typography.
Slack Bots and Custom Unfurling Overrides
Slack's API allows bots and apps to override the default unfurling behavior with custom attachment blocks. If you are building an integration that shares links programmatically, you have far more control over the preview card than relying on OG tags alone. However, for organic link sharing by humans in channels, OG tags are still the primary source. Some Slack apps like Notion, Figma, and GitHub provide their own custom unfurling, which is why their links look richer than standard web pages. If your product's links are frequently shared in Slack, consider building a custom Slack unfurl handler that pulls real-time data and renders a more informative card than static OG tags can provide.
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