diff --git a/js/social-threads.js b/js/social-threads.js
new file mode 100644
index 0000000..1a84836
--- /dev/null
+++ b/js/social-threads.js
@@ -0,0 +1,134 @@
+/**
+ * Social Threads — Alpine.js unified component for Bluesky + Mastodon/AP replies
+ * Used in webmentions.njk Replies section to fetch live thread data from both platforms.
+ */
+document.addEventListener("alpine:init", () => {
+  Alpine.data("socialReplies", (bskyUrl, postUrl, mastodonInstance, apIdentity) => ({
+    bskyReplies: [],
+    mastodonReplies: [],
+    loading: true,
+
+    async init() {
+      const tasks = [];
+      if (bskyUrl) tasks.push(this._fetchBsky(bskyUrl));
+      if (mastodonInstance && apIdentity) tasks.push(this._fetchMastodon(postUrl, mastodonInstance, apIdentity));
+      await Promise.allSettled(tasks);
+      this.loading = false;
+    },
+
+    // ── Bluesky / AT Protocol ──────────────────────────────────────────────
+
+    async _fetchBsky(url) {
+      try {
+        const match = url.match(/bsky\.app\/profile\/([^/?#]+)\/post\/([^/?#]+)/);
+        if (!match) return;
+        const [, actor, rkey] = match;
+        const atUri = `at://${actor}/app.bsky.feed.post/${rkey}`;
+        const res = await fetch(
+          `https://public.api.bsky.app/xrpc/app.bsky.feed.getPostThread?uri=${encodeURIComponent(atUri)}&depth=10`
+        );
+        if (!res.ok) return;
+        const data = await res.json();
+        this.bskyReplies = this._flattenBsky(data.thread, 0);
+      } catch {
+        // fail silently — no replies shown
+      }
+    },
+
+    _flattenBsky(node, depth) {
+      const out = [];
+      for (const r of node.replies || []) {
+        if (r.$type !== "app.bsky.feed.defs#threadViewPost") continue;
+        const p = r.post;
+        const rkey = p.uri.split("/").pop();
+        out.push({
+          depth: Math.min(depth, 3),
+          uri: p.uri,
+          url: `https://bsky.app/profile/${p.author.handle}/post/${rkey}`,
+          author: {
+            name: p.author.displayName || p.author.handle,
+            handle: p.author.handle,
+            avatar: p.author.avatar || "",
+            url: `https://bsky.app/profile/${p.author.handle}`,
+          },
+          text: p.record.text,
+          published: p.record.createdAt,
+          likeCount: p.likeCount || 0,
+        });
+        out.push(...this._flattenBsky(r, depth + 1));
+      }
+      return out;
+    },
+
+    // ── Mastodon / ActivityPub ─────────────────────────────────────────────
+
+    async _fetchMastodon(postUrl, instance, apIdentity) {
+      try {
+        // Parse "@handle@domain" from apIdentity
+        const m = apIdentity.match(/^@?([^@]+)@(.+)$/);
+        if (!m) return;
+        const [, handle, domain] = m;
+        const acct = encodeURIComponent(`${handle}@${domain}`);
+
+        // Look up the blog's AP actor on the Mastodon instance
+        const lookupRes = await fetch(`https://${instance}/api/v1/accounts/lookup?acct=${acct}`);
+        if (!lookupRes.ok) return;
+        const account = await lookupRes.json();
+
+        // Find the status matching the post URL
+        const statusId = await this._findMastodonStatus(account.id, postUrl, instance);
+        if (!statusId) return;
+
+        // Fetch thread context
+        const ctxRes = await fetch(`https://${instance}/api/v1/statuses/${statusId}/context`);
+        if (!ctxRes.ok) return;
+        const ctx = await ctxRes.json();
+
+        this.mastodonReplies = (ctx.descendants || []).map((s) => ({
+          id: s.id,
+          url: s.url,
+          author: {
+            name: s.account.display_name || s.account.username,
+            handle: s.account.acct,
+            avatar: s.account.avatar || "",
+            url: s.account.url,
+          },
+          content: s.content, // HTML from Mastodon
+          published: s.created_at,
+          favourites: s.favourites_count || 0,
+        }));
+      } catch {
+        // fail silently
+      }
+    },
+
+    async _findMastodonStatus(accountId, postUrl, instance) {
+      let maxId = null;
+      for (let page = 0; page < 10; page++) {
+        const qs = `limit=40${maxId ? `&max_id=${maxId}` : ""}`;
+        const res = await fetch(`https://${instance}/api/v1/accounts/${accountId}/statuses?${qs}`);
+        if (!res.ok) break;
+        const statuses = await res.json();
+        if (!Array.isArray(statuses) || !statuses.length) break;
+        const match = statuses.find((s) => s.url === postUrl);
+        if (match) return match.id;
+        maxId = statuses[statuses.length - 1].id;
+      }
+      return null;
+    },
+
+    // ── Utilities ─────────────────────────────────────────────────────────
+
+    formatDate(dateStr) {
+      try {
+        return new Date(dateStr).toLocaleDateString("de-DE", {
+          day: "numeric",
+          month: "long",
+          year: "numeric",
+        });
+      } catch {
+        return dateStr;
+      }
+    },
+  }));
+});