diff --git a/README.md b/README.md
index 2bcf8a1..15b13b7 100644
--- a/README.md
+++ b/README.md
@@ -74,6 +74,28 @@ Both functions authenticate with a scoped `email + crm` key held by the paused
 agent runs nothing. It exists only because an API key cannot mint another API
 key. Deleting it revokes the key and breaks both functions.
 
+## Sharing
+
+`/flyer` (`views/flyer.ejs`) is the link to send someone: the poster shown as a
+sheet, a download button, and the share controls. It is what the footer and the
+post-RSVP confirmation both point at, rather than the raw PDF, so a share always
+lands on something with context.
+
+There is no general "share protocol". What exists is the **Web Share API**
+(`navigator.share`), which on a phone opens the real OS share sheet and is the
+only way to reach apps a web page cannot link to. Where `navigator.canShare`
+allows files it shares the PDF itself, which is far better in a group chat than
+a link; it falls back to sharing the URL, and the button stays hidden entirely on
+browsers without support. Under that sit plain per-channel URLs (SMS, mailto,
+WhatsApp, X, LinkedIn, Facebook) that work with no JavaScript at all, and a
+copy-to-clipboard with a select-the-text fallback for in-app browsers that block
+the clipboard.
+
+`site.config.js -> images.share` is a 1200x630 unfurl card carrying the same four
+facts the flyer leads with. Both `/` and `/flyer` use it for `og:image`, so a
+pasted link never previews as a wordless photo. Regenerate it from
+`design/og-card.html` the same way as the flyer.
+
 ## The printable flyer
 
 `public/assets/founders-break-flyer.pdf` is a one-page US Letter flyer, linked
diff --git a/design/email-header-web.png b/design/email-header-web.png
new file mode 100644
index 0000000..5d6cf2d
Binary files /dev/null and b/design/email-header-web.png differ
diff --git a/design/og-card.html b/design/og-card.html
new file mode 100644
index 0000000..fc2ef61
--- /dev/null
+++ b/design/og-card.html
@@ -0,0 +1,48 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8">
+<link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&family=Space+Grotesk:wght@600;700&family=JetBrains+Mono:wght@500&display=swap" rel="stylesheet">
+<style>
+  /* 1200x630 unfurl card. This is what people actually see when the link is
+     pasted into a text, a Slack channel or a story, so it carries the same four
+     facts the flyer leads with rather than being a decorative banner. */
+  * { box-sizing: border-box; margin: 0; padding: 0; }
+  body { width: 1200px; height: 630px; background: #06060b; color: #f1f0ff;
+         font-family: "Inter", sans-serif; overflow: hidden; position: relative; }
+
+  .art { position: absolute; top: -40px; right: -260px; width: 900px; opacity: 0.22; }
+  .art img { width: 100%; display: block; }
+
+  .wrap { position: relative; padding: 64px 68px; height: 630px; display: flex; flex-direction: column; }
+
+  .kicker { font-family: "JetBrains Mono", monospace; font-size: 15px; letter-spacing: 0.2em;
+            text-transform: uppercase; color: #34d399; }
+  h1 { font-family: "Space Grotesk", sans-serif; font-size: 88px; font-weight: 700;
+       line-height: 0.9; letter-spacing: -0.035em; margin-top: 22px; text-transform: uppercase; }
+
+  .when { margin-top: 34px; display: flex; align-items: baseline; gap: 18px; }
+  .when b { font-family: "Space Grotesk", sans-serif; font-size: 40px; font-weight: 700;
+            letter-spacing: -0.02em; text-transform: uppercase; }
+  .when .t { color: #34d399; }
+
+  .foot { margin-top: auto; display: flex; align-items: flex-end; justify-content: space-between; }
+  .where { font-size: 21px; color: #c2c0d4; line-height: 1.4; }
+  .where strong { color: #f1f0ff; font-weight: 600; display: block; font-size: 24px; }
+  .free { font-family: "JetBrains Mono", monospace; font-size: 15px; letter-spacing: 0.16em;
+          text-transform: uppercase; color: #8b89a6; text-align: right; line-height: 1.7; }
+</style>
+</head>
+<body>
+  <div class="art"><img src="email-header-web.png" alt=""></div>
+  <div class="wrap">
+    <p class="kicker">UF Startup Pool Social &nbsp;/&nbsp; Gainesville</p>
+    <h1>The Founder&rsquo;s<br>Break</h1>
+    <p class="when"><b>Every Thursday</b><b class="t">7 to 9 PM</b></p>
+    <div class="foot">
+      <p class="where"><strong>Silver Q Billiards</strong>225 W University Ave, Gainesville</p>
+      <p class="free">Free entry<br>18 and over</p>
+    </div>
+  </div>
+</body>
+</html>