diff --git a/js/app.js b/js/app.js
index 772baeba..25587992 100644
--- a/js/app.js
+++ b/js/app.js
@@ -150,6 +150,7 @@ import {
   urlHealthConstants,
 } from "./state/cache.js";
 import ApplicationBootstrap from "./ui/applicationBootstrap.js";
+import SimilarContentController from "./ui/similarContentController.js";
 import VideoModalCommentController from "./ui/videoModalCommentController.js";
 import TorrentStatusController from "./ui/torrentStatusController.js";
 import ModerationActionController from "./services/moderationActionController.js";
@@ -285,6 +286,7 @@ class Application {
     });
 
     this.initializeModerationActionController();
+    this.initializeSimilarContentController();
   }
 
   get modalVideo() {
@@ -1136,7 +1138,40 @@ class Application {
     };
   }
 
+  initializeSimilarContentController() {
+    if (this.similarContentController) {
+      return;
+    }
+
+    this.similarContentController = new SimilarContentController({
+      services: {
+        nostrClient,
+      },
+      callbacks: {
+        isAuthorBlocked: (pubkey) => this.isAuthorBlocked(pubkey),
+        decorateVideoModeration: (video) => this.decorateVideoModeration(video),
+        decorateVideoCreatorIdentity: (video) => this.decorateVideoCreatorIdentity(video),
+      },
+      ui: {
+        videoModal: this.videoModal,
+      },
+      state: {
+        getVideoListView: () => this.videoListView,
+        getVideosMap: () => this.videosMap,
+      },
+      helpers: {
+        getKnownVideoPostedAt: (video) => this.getKnownVideoPostedAt(video),
+        buildShareUrlFromEventId: (id) => this.buildShareUrlFromEventId(id),
+        formatTimeAgo: (ts) => this.formatTimeAgo(ts),
+      }
+    });
+  }
+
   extractDTagValue(tags) {
+    if (this.similarContentController) {
+      return this.similarContentController.extractDTagValue(tags);
+    }
+    // Fallback if controller not initialized (though it should be)
     if (!Array.isArray(tags)) {
       return "";
     }
@@ -1152,6 +1187,10 @@ class Application {
   }
 
   deriveVideoPointerInfo(video) {
+    if (this.similarContentController) {
+      return this.similarContentController.deriveVideoPointerInfo(video);
+    }
+    // Fallback if controller not initialized
     if (!video || typeof video !== "object") {
       return null;
     }
@@ -1168,271 +1207,20 @@ class Application {
     });
   }
 
-  computeSimilarContentCandidates({ activeVideo = this.currentVideo, maxItems = 5 } = {}) {
-    const decorateCandidate = (video) => {
-      if (!video || typeof video !== "object") {
-        return video;
-      }
-      let decoratedVideo = video;
-      if (typeof this.decorateVideoModeration === "function") {
-        try {
-          const decorated = this.decorateVideoModeration(video);
-          if (decorated && typeof decorated === "object") {
-            decoratedVideo = decorated;
-          }
-        } catch (error) {
-          devLogger.warn(
-            "[Application] Failed to decorate similar content candidate",
-            error,
-          );
-        }
-      }
-      if (typeof this.decorateVideoCreatorIdentity === "function") {
-        try {
-          const identityDecorated = this.decorateVideoCreatorIdentity(
-            decoratedVideo,
-          );
-          if (identityDecorated && typeof identityDecorated === "object") {
-            decoratedVideo = identityDecorated;
-          }
-        } catch (error) {
-          devLogger.warn(
-            "[Application] Failed to decorate similar content identity",
-            error,
-          );
-        }
-      }
-      return decoratedVideo;
-    };
-
-    const target = activeVideo && typeof activeVideo === "object" ? decorateCandidate(activeVideo) : null;
-    if (!target) {
-      return [];
-    }
-
-    const activeTagsSource = Array.isArray(target.displayTags) && target.displayTags.length
-      ? target.displayTags
-      : collectVideoTags(target);
-
-    const activeTagSet = new Set();
-    for (const tag of activeTagsSource) {
-      if (typeof tag !== "string") {
-        continue;
-      }
-      const normalized = tag.trim().toLowerCase();
-      if (normalized) {
-        activeTagSet.add(normalized);
-      }
-    }
-
-    if (activeTagSet.size === 0) {
-      return [];
-    }
-
-    const limit = Number.isFinite(maxItems) && maxItems > 0
-      ? Math.max(1, Math.floor(maxItems))
-      : 5;
-
-    let candidateSource = [];
-    if (Array.isArray(this.videoListView?.currentVideos) && this.videoListView.currentVideos.length) {
-      candidateSource = this.videoListView.currentVideos;
-    } else if (this.videosMap instanceof Map && this.videosMap.size) {
-      candidateSource = Array.from(this.videosMap.values());
-    } else if (nostrClient && typeof nostrClient.getActiveVideos === "function") {
-      try {
-        const activeVideos = nostrClient.getActiveVideos();
-        if (Array.isArray(activeVideos)) {
-          candidateSource = activeVideos;
-        }
-      } catch (error) {
-        devLogger.warn("[Application] Failed to read active videos for similar content:", error);
-      }
-    }
-
-    if (!Array.isArray(candidateSource) || candidateSource.length === 0) {
-      return [];
-    }
-
-    const activeId = typeof target.id === "string" ? target.id : "";
-    const activePointerKey = typeof target.pointerKey === "string" ? target.pointerKey : "";
-    const seenKeys = new Set();
-    if (activeId) {
-      const normalizedId = activeId.trim().toLowerCase();
-      if (normalizedId) {
-        seenKeys.add(normalizedId);
-      }
-    }
-    if (activePointerKey) {
-      const normalizedPointer = activePointerKey.trim().toLowerCase();
-      if (normalizedPointer) {
-        seenKeys.add(normalizedPointer);
-      }
-    }
-
-    const results = [];
-
-    for (const candidate of candidateSource) {
-      const decoratedCandidate = decorateCandidate(candidate);
-      if (!decoratedCandidate || typeof decoratedCandidate !== "object") {
-        continue;
-      }
-      if (decoratedCandidate === target) {
-        continue;
-      }
-
-      const candidateId = typeof decoratedCandidate.id === "string" ? decoratedCandidate.id : "";
-      if (candidateId && candidateId === activeId) {
-        continue;
-      }
-      if (decoratedCandidate.deleted === true) {
-        continue;
-      }
-      if (decoratedCandidate.isPrivate === true) {
-        continue;
-      }
-      if (decoratedCandidate.isNsfw === true && ALLOW_NSFW_CONTENT !== true) {
-        continue;
-      }
-
-      const candidatePubkey = typeof decoratedCandidate.pubkey === "string" ? decoratedCandidate.pubkey : "";
-      if (candidatePubkey && this.isAuthorBlocked(candidatePubkey)) {
-        continue;
-      }
-
-      const candidateTagsSource = Array.isArray(decoratedCandidate.displayTags) && decoratedCandidate.displayTags.length
-        ? decoratedCandidate.displayTags
-        : collectVideoTags(decoratedCandidate);
-      if (!Array.isArray(candidateTagsSource) || candidateTagsSource.length === 0) {
-        continue;
-      }
-
-      const candidateTagSet = new Set();
-      for (const tag of candidateTagsSource) {
-        if (typeof tag !== "string") {
-          continue;
-        }
-        const normalized = tag.trim().toLowerCase();
-        if (normalized) {
-          candidateTagSet.add(normalized);
-        }
-      }
-
-      if (candidateTagSet.size === 0) {
-        continue;
-      }
-
-      let sharedCount = 0;
-      for (const tag of candidateTagSet) {
-        if (activeTagSet.has(tag)) {
-          sharedCount += 1;
-        }
-      }
-
-      if (sharedCount === 0) {
-        continue;
-      }
-
-      const pointerInfo = this.deriveVideoPointerInfo(candidate);
-      const pointerKey = typeof candidate.pointerKey === "string" && candidate.pointerKey.trim()
-        ? candidate.pointerKey.trim()
-        : typeof pointerInfo?.key === "string" && pointerInfo.key
-          ? pointerInfo.key
-          : "";
-
-      const dedupeKeyRaw = (candidateId || pointerKey || "").trim();
-      if (dedupeKeyRaw) {
-        const dedupeKey = dedupeKeyRaw.toLowerCase();
-        if (seenKeys.has(dedupeKey)) {
-          continue;
-        }
-        seenKeys.add(dedupeKey);
-      }
-
-      if (!Array.isArray(candidate.displayTags) || candidate.displayTags.length === 0) {
-        candidate.displayTags = Array.isArray(candidateTagsSource)
-          ? candidateTagsSource.slice()
-          : [];
-      }
-
-      let postedAt = this.getKnownVideoPostedAt(decoratedCandidate);
-      if (!Number.isFinite(postedAt) && Number.isFinite(decoratedCandidate.rootCreatedAt)) {
-        postedAt = Math.floor(decoratedCandidate.rootCreatedAt);
-      }
-      if (!Number.isFinite(postedAt) && Number.isFinite(decoratedCandidate.created_at)) {
-        postedAt = Math.floor(decoratedCandidate.created_at);
-      }
-      if (!Number.isFinite(postedAt)) {
-        postedAt = null;
-      }
-
-      let shareUrl = "";
-      if (typeof decoratedCandidate.shareUrl === "string" && decoratedCandidate.shareUrl.trim()) {
-        shareUrl = decoratedCandidate.shareUrl.trim();
-      } else if (candidateId) {
-        shareUrl = this.buildShareUrlFromEventId(candidateId) || "";
-      }
-
-      results.push({
-        video: decoratedCandidate,
-        pointerInfo: pointerInfo || null,
-        shareUrl,
-        postedAt,
-        sharedTagCount: sharedCount,
+  computeSimilarContentCandidates(options = {}) {
+    if (this.similarContentController) {
+      return this.similarContentController.computeCandidates({
+        activeVideo: options.activeVideo || this.currentVideo,
+        maxItems: options.maxItems,
       });
     }
-
-    if (results.length === 0) {
-      return [];
-    }
-
-    results.sort((a, b) => {
-      if (b.sharedTagCount !== a.sharedTagCount) {
-        return b.sharedTagCount - a.sharedTagCount;
-      }
-      const tsA = Number.isFinite(a.postedAt) ? a.postedAt : 0;
-      const tsB = Number.isFinite(b.postedAt) ? b.postedAt : 0;
-      return tsB - tsA;
-    });
-
-    return results.slice(0, limit).map((entry) => {
-      const normalizedPostedAt = Number.isFinite(entry.postedAt)
-        ? Math.floor(entry.postedAt)
-        : null;
-      const timeAgo = normalizedPostedAt !== null ? this.formatTimeAgo(normalizedPostedAt) : "";
-      return {
-        video: entry.video,
-        pointerInfo: entry.pointerInfo,
-        shareUrl: entry.shareUrl,
-        postedAt: normalizedPostedAt,
-        timeAgo,
-        sharedTagCount: entry.sharedTagCount,
-      };
-    });
+    return [];
   }
 
   updateModalSimilarContent({ activeVideo = this.currentVideo, maxItems } = {}) {
-    if (!this.videoModal) {
-      return;
-    }
-
-    const target = activeVideo && typeof activeVideo === "object" ? activeVideo : null;
-    if (!target) {
-      if (typeof this.videoModal.clearSimilarContent === "function") {
-        this.videoModal.clearSimilarContent();
-      }
-      return;
-    }
-
-    const matches = this.computeSimilarContentCandidates({ activeVideo: target, maxItems });
-    if (matches.length > 0) {
-      if (typeof this.videoModal.setSimilarContent === "function") {
-        this.videoModal.setSimilarContent(matches);
-      }
-      return;
-    }
-
-    if (typeof this.videoModal.clearSimilarContent === "function") {
-      this.videoModal.clearSimilarContent();
+    if (this.similarContentController) {
+      this.similarContentController.ui.videoModal = this.videoModal;
+      this.similarContentController.updateModal({ activeVideo, maxItems });
     }
   }
 
diff --git a/js/ui/similarContentController.js b/js/ui/similarContentController.js
new file mode 100644
index 00000000..cfc60e74
--- /dev/null
+++ b/js/ui/similarContentController.js
@@ -0,0 +1,332 @@
+import { devLogger } from "../utils/logger.js";
+import { collectVideoTags } from "../utils/videoTags.js";
+import { ALLOW_NSFW_CONTENT } from "../config.js";
+import resolveVideoPointer from "../utils/videoPointer.js";
+
+/**
+ * Controller for managing "Similar Content" logic and updates for the video modal.
+ */
+export default class SimilarContentController {
+  constructor({
+    services = {},
+    callbacks = {},
+    ui = {},
+    state = {},
+    helpers = {}
+  }) {
+    this.services = services;
+    this.callbacks = callbacks;
+    this.ui = ui;
+    this.state = state;
+    this.helpers = helpers;
+  }
+
+  extractDTagValue(tags) {
+    if (!Array.isArray(tags)) {
+      return "";
+    }
+    for (const tag of tags) {
+      if (!Array.isArray(tag) || tag.length < 2) {
+        continue;
+      }
+      if (tag[0] === "d" && typeof tag[1] === "string") {
+        return tag[1];
+      }
+    }
+    return "";
+  }
+
+  deriveVideoPointerInfo(video) {
+    if (!video || typeof video !== "object") {
+      return null;
+    }
+
+    const dTagValue = (this.extractDTagValue(video.tags) || "").trim();
+
+    return resolveVideoPointer({
+      kind: video.kind,
+      pubkey: video.pubkey,
+      videoRootId: video.videoRootId,
+      dTag: dTagValue,
+      fallbackEventId: video.id,
+      relay: video.relay,
+    });
+  }
+
+  computeCandidates({ activeVideo, maxItems = 5 } = {}) {
+    const decorateCandidate = (video) => {
+      if (!video || typeof video !== "object") {
+        return video;
+      }
+      let decoratedVideo = video;
+      if (typeof this.callbacks.decorateVideoModeration === "function") {
+        try {
+          const decorated = this.callbacks.decorateVideoModeration(video);
+          if (decorated && typeof decorated === "object") {
+            decoratedVideo = decorated;
+          }
+        } catch (error) {
+          devLogger.warn(
+            "[SimilarContentController] Failed to decorate similar content candidate",
+            error,
+          );
+        }
+      }
+      if (typeof this.callbacks.decorateVideoCreatorIdentity === "function") {
+        try {
+          const identityDecorated = this.callbacks.decorateVideoCreatorIdentity(
+            decoratedVideo,
+          );
+          if (identityDecorated && typeof identityDecorated === "object") {
+            decoratedVideo = identityDecorated;
+          }
+        } catch (error) {
+          devLogger.warn(
+            "[SimilarContentController] Failed to decorate similar content identity",
+            error,
+          );
+        }
+      }
+      return decoratedVideo;
+    };
+
+    const target = activeVideo && typeof activeVideo === "object" ? decorateCandidate(activeVideo) : null;
+    if (!target) {
+      return [];
+    }
+
+    const activeTagsSource = Array.isArray(target.displayTags) && target.displayTags.length
+      ? target.displayTags
+      : collectVideoTags(target);
+
+    const activeTagSet = new Set();
+    for (const tag of activeTagsSource) {
+      if (typeof tag !== "string") {
+        continue;
+      }
+      const normalized = tag.trim().toLowerCase();
+      if (normalized) {
+        activeTagSet.add(normalized);
+      }
+    }
+
+    if (activeTagSet.size === 0) {
+      return [];
+    }
+
+    const limit = Number.isFinite(maxItems) && maxItems > 0
+      ? Math.max(1, Math.floor(maxItems))
+      : 5;
+
+    let candidateSource = [];
+    const videoListView = this.state.getVideoListView ? this.state.getVideoListView() : null;
+    const videosMap = this.state.getVideosMap ? this.state.getVideosMap() : null;
+    const nostrClient = this.services.nostrClient;
+
+    if (videoListView && Array.isArray(videoListView.currentVideos) && videoListView.currentVideos.length) {
+      candidateSource = videoListView.currentVideos;
+    } else if (videosMap instanceof Map && videosMap.size) {
+      candidateSource = Array.from(videosMap.values());
+    } else if (nostrClient && typeof nostrClient.getActiveVideos === "function") {
+      try {
+        const activeVideos = nostrClient.getActiveVideos();
+        if (Array.isArray(activeVideos)) {
+          candidateSource = activeVideos;
+        }
+      } catch (error) {
+        devLogger.warn("[SimilarContentController] Failed to read active videos for similar content:", error);
+      }
+    }
+
+    if (!Array.isArray(candidateSource) || candidateSource.length === 0) {
+      return [];
+    }
+
+    const activeId = typeof target.id === "string" ? target.id : "";
+    const activePointerKey = typeof target.pointerKey === "string" ? target.pointerKey : "";
+    const seenKeys = new Set();
+    if (activeId) {
+      const normalizedId = activeId.trim().toLowerCase();
+      if (normalizedId) {
+        seenKeys.add(normalizedId);
+      }
+    }
+    if (activePointerKey) {
+      const normalizedPointer = activePointerKey.trim().toLowerCase();
+      if (normalizedPointer) {
+        seenKeys.add(normalizedPointer);
+      }
+    }
+
+    const results = [];
+
+    for (const candidate of candidateSource) {
+      const decoratedCandidate = decorateCandidate(candidate);
+      if (!decoratedCandidate || typeof decoratedCandidate !== "object") {
+        continue;
+      }
+      if (decoratedCandidate === target) {
+        continue;
+      }
+
+      const candidateId = typeof decoratedCandidate.id === "string" ? decoratedCandidate.id : "";
+      if (candidateId && candidateId === activeId) {
+        continue;
+      }
+      if (decoratedCandidate.deleted === true) {
+        continue;
+      }
+      if (decoratedCandidate.isPrivate === true) {
+        continue;
+      }
+      if (decoratedCandidate.isNsfw === true && ALLOW_NSFW_CONTENT !== true) {
+        continue;
+      }
+
+      const candidatePubkey = typeof decoratedCandidate.pubkey === "string" ? decoratedCandidate.pubkey : "";
+      if (candidatePubkey && typeof this.callbacks.isAuthorBlocked === "function" && this.callbacks.isAuthorBlocked(candidatePubkey)) {
+        continue;
+      }
+
+      const candidateTagsSource = Array.isArray(decoratedCandidate.displayTags) && decoratedCandidate.displayTags.length
+        ? decoratedCandidate.displayTags
+        : collectVideoTags(decoratedCandidate);
+      if (!Array.isArray(candidateTagsSource) || candidateTagsSource.length === 0) {
+        continue;
+      }
+
+      const candidateTagSet = new Set();
+      for (const tag of candidateTagsSource) {
+        if (typeof tag !== "string") {
+          continue;
+        }
+        const normalized = tag.trim().toLowerCase();
+        if (normalized) {
+          candidateTagSet.add(normalized);
+        }
+      }
+
+      if (candidateTagSet.size === 0) {
+        continue;
+      }
+
+      let sharedCount = 0;
+      for (const tag of candidateTagSet) {
+        if (activeTagSet.has(tag)) {
+          sharedCount += 1;
+        }
+      }
+
+      if (sharedCount === 0) {
+        continue;
+      }
+
+      const pointerInfo = this.deriveVideoPointerInfo(candidate);
+      const pointerKey = typeof candidate.pointerKey === "string" && candidate.pointerKey.trim()
+        ? candidate.pointerKey.trim()
+        : typeof pointerInfo?.key === "string" && pointerInfo.key
+          ? pointerInfo.key
+          : "";
+
+      const dedupeKeyRaw = (candidateId || pointerKey || "").trim();
+      if (dedupeKeyRaw) {
+        const dedupeKey = dedupeKeyRaw.toLowerCase();
+        if (seenKeys.has(dedupeKey)) {
+          continue;
+        }
+        seenKeys.add(dedupeKey);
+      }
+
+      if (!Array.isArray(candidate.displayTags) || candidate.displayTags.length === 0) {
+        candidate.displayTags = Array.isArray(candidateTagsSource)
+          ? candidateTagsSource.slice()
+          : [];
+      }
+
+      let postedAt = null;
+      if (typeof this.helpers.getKnownVideoPostedAt === "function") {
+          postedAt = this.helpers.getKnownVideoPostedAt(decoratedCandidate);
+      }
+      if (!Number.isFinite(postedAt) && Number.isFinite(decoratedCandidate.rootCreatedAt)) {
+        postedAt = Math.floor(decoratedCandidate.rootCreatedAt);
+      }
+      if (!Number.isFinite(postedAt) && Number.isFinite(decoratedCandidate.created_at)) {
+        postedAt = Math.floor(decoratedCandidate.created_at);
+      }
+      if (!Number.isFinite(postedAt)) {
+        postedAt = null;
+      }
+
+      let shareUrl = "";
+      if (typeof decoratedCandidate.shareUrl === "string" && decoratedCandidate.shareUrl.trim()) {
+        shareUrl = decoratedCandidate.shareUrl.trim();
+      } else if (candidateId && typeof this.helpers.buildShareUrlFromEventId === "function") {
+        shareUrl = this.helpers.buildShareUrlFromEventId(candidateId) || "";
+      }
+
+      results.push({
+        video: decoratedCandidate,
+        pointerInfo: pointerInfo || null,
+        shareUrl,
+        postedAt,
+        sharedTagCount: sharedCount,
+      });
+    }
+
+    if (results.length === 0) {
+      return [];
+    }
+
+    results.sort((a, b) => {
+      if (b.sharedTagCount !== a.sharedTagCount) {
+        return b.sharedTagCount - a.sharedTagCount;
+      }
+      const tsA = Number.isFinite(a.postedAt) ? a.postedAt : 0;
+      const tsB = Number.isFinite(b.postedAt) ? b.postedAt : 0;
+      return tsB - tsA;
+    });
+
+    return results.slice(0, limit).map((entry) => {
+      const normalizedPostedAt = Number.isFinite(entry.postedAt)
+        ? Math.floor(entry.postedAt)
+        : null;
+      const timeAgo = normalizedPostedAt !== null && typeof this.helpers.formatTimeAgo === "function"
+        ? this.helpers.formatTimeAgo(normalizedPostedAt)
+        : "";
+      return {
+        video: entry.video,
+        pointerInfo: entry.pointerInfo,
+        shareUrl: entry.shareUrl,
+        postedAt: normalizedPostedAt,
+        timeAgo,
+        sharedTagCount: entry.sharedTagCount,
+      };
+    });
+  }
+
+  updateModal({ activeVideo, maxItems } = {}) {
+    if (!this.ui.videoModal) {
+      return;
+    }
+
+    const target = activeVideo && typeof activeVideo === "object" ? activeVideo : null;
+    if (!target) {
+      if (typeof this.ui.videoModal.clearSimilarContent === "function") {
+        this.ui.videoModal.clearSimilarContent();
+      }
+      return;
+    }
+
+    const matches = this.computeCandidates({ activeVideo: target, maxItems });
+    if (matches.length > 0) {
+      if (typeof this.ui.videoModal.setSimilarContent === "function") {
+        this.ui.videoModal.setSimilarContent(matches);
+      }
+      return;
+    }
+
+    if (typeof this.ui.videoModal.clearSimilarContent === "function") {
+      this.ui.videoModal.clearSimilarContent();
+    }
+  }
+}
diff --git a/tests/ui/similarContentController.test.mjs b/tests/ui/similarContentController.test.mjs
new file mode 100644
index 00000000..3c339642
--- /dev/null
+++ b/tests/ui/similarContentController.test.mjs
@@ -0,0 +1,164 @@
+
+import { describe, it, mock, beforeEach } from "node:test";
+import assert from "node:assert";
+import SimilarContentController from "../../js/ui/similarContentController.js";
+
+describe("SimilarContentController", () => {
+  let controller;
+  let services;
+  let callbacks;
+  let ui;
+  let state;
+  let helpers;
+
+  beforeEach(() => {
+    services = {
+      nostrClient: {
+        getActiveVideos: mock.fn(() => []),
+      },
+    };
+    callbacks = {
+      isAuthorBlocked: mock.fn(() => false),
+      decorateVideoModeration: mock.fn((v) => v),
+      decorateVideoCreatorIdentity: mock.fn((v) => v),
+    };
+    ui = {
+      videoModal: {
+        setSimilarContent: mock.fn(),
+        clearSimilarContent: mock.fn(),
+      },
+    };
+    state = {
+      getVideoListView: mock.fn(() => ({ currentVideos: [] })),
+      getVideosMap: mock.fn(() => new Map()),
+    };
+    helpers = {
+      getKnownVideoPostedAt: mock.fn(() => Date.now()),
+      buildShareUrlFromEventId: mock.fn((id) => `https://example.com/v/${id}`),
+      formatTimeAgo: mock.fn(() => "just now"),
+    };
+
+    controller = new SimilarContentController({
+      services,
+      callbacks,
+      ui,
+      state,
+      helpers,
+    });
+  });
+
+  describe("extractDTagValue", () => {
+    it("should return the 'd' tag value", () => {
+      const tags = [["e", "123"], ["d", "my-d-tag"]];
+      const result = controller.extractDTagValue(tags);
+      assert.strictEqual(result, "my-d-tag");
+    });
+
+    it("should return empty string if no 'd' tag", () => {
+        const tags = [["e", "123"]];
+        const result = controller.extractDTagValue(tags);
+        assert.strictEqual(result, "");
+    });
+  });
+
+  describe("computeCandidates", () => {
+    it("should return empty array if no active video", () => {
+      const result = controller.computeCandidates();
+      assert.deepStrictEqual(result, []);
+    });
+
+    it("should compute similar candidates based on tags", () => {
+        const activeVideo = {
+            id: "active",
+            displayTags: ["fun", "music"],
+            pubkey: "abc"
+        };
+        const candidate1 = {
+            id: "c1",
+            displayTags: ["fun", "other"],
+            pubkey: "def"
+        };
+        const candidate2 = {
+            id: "c2",
+            displayTags: ["boring"],
+            pubkey: "ghi"
+        };
+
+        state.getVideoListView.mock.mockImplementationOnce(() => ({
+            currentVideos: [candidate1, candidate2]
+        }));
+
+        const result = controller.computeCandidates({ activeVideo });
+
+        assert.strictEqual(result.length, 1);
+        assert.strictEqual(result[0].video.id, "c1");
+        assert.strictEqual(result[0].sharedTagCount, 1);
+    });
+
+    it("should exclude blocked authors", () => {
+        const activeVideo = { id: "active", displayTags: ["fun"] };
+        const candidate1 = { id: "c1", displayTags: ["fun"], pubkey: "bad-guy" };
+
+        state.getVideoListView.mock.mockImplementationOnce(() => ({
+            currentVideos: [candidate1]
+        }));
+
+        callbacks.isAuthorBlocked.mock.mockImplementationOnce((pubkey) => pubkey === "bad-guy");
+
+        const result = controller.computeCandidates({ activeVideo });
+        assert.strictEqual(result.length, 0);
+    });
+
+    it("should prioritize higher shared tag count", () => {
+        const activeVideo = { id: "active", displayTags: ["a", "b", "c"] };
+        const candidate1 = { id: "c1", displayTags: ["a"] };
+        const candidate2 = { id: "c2", displayTags: ["a", "b"] };
+
+        state.getVideoListView.mock.mockImplementationOnce(() => ({
+            currentVideos: [candidate1, candidate2]
+        }));
+
+        const result = controller.computeCandidates({ activeVideo });
+        assert.strictEqual(result.length, 2);
+        assert.strictEqual(result[0].video.id, "c2"); // 2 shared tags
+        assert.strictEqual(result[1].video.id, "c1"); // 1 shared tag
+    });
+  });
+
+  describe("updateModal", () => {
+    it("should clear similar content if no active video", () => {
+        controller.updateModal();
+        assert.strictEqual(ui.videoModal.clearSimilarContent.mock.callCount(), 1);
+    });
+
+    it("should set similar content if matches found", () => {
+        const activeVideo = { id: "active", displayTags: ["fun"] };
+        const candidate1 = { id: "c1", displayTags: ["fun"] };
+
+        state.getVideoListView.mock.mockImplementationOnce(() => ({
+            currentVideos: [candidate1]
+        }));
+
+        controller.updateModal({ activeVideo });
+
+        assert.strictEqual(ui.videoModal.setSimilarContent.mock.callCount(), 1);
+        const args = ui.videoModal.setSimilarContent.mock.calls[0].arguments;
+        assert.strictEqual(args[0].length, 1);
+        assert.strictEqual(args[0][0].video.id, "c1");
+    });
+
+    it("should clear similar content if no matches found", () => {
+        const activeVideo = { id: "active", displayTags: ["fun"] };
+        const candidate1 = { id: "c1", displayTags: ["boring"] };
+
+        state.getVideoListView.mock.mockImplementationOnce(() => ({
+            currentVideos: [candidate1]
+        }));
+
+        controller.updateModal({ activeVideo });
+
+        assert.strictEqual(ui.videoModal.clearSimilarContent.mock.callCount(), 1);
+    });
+  });
+
+});