diff --git a/package.json b/package.json
index fdf13df..07b2af8 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,8 @@
   "description": "All-in-one sentence mining overlay with AnkiConnect and dictionary integration",
   "main": "dist/main.js",
   "scripts": {
-    "build": "tsc && tsc -p tsconfig.renderer.json && cp src/renderer/index.html src/renderer/style.css dist/renderer/ && bash scripts/build-macos-helper.sh",
+    "build": "tsc && pnpm run build:renderer && cp src/renderer/index.html src/renderer/style.css dist/renderer/ && bash scripts/build-macos-helper.sh",
+    "build:renderer": "esbuild src/renderer/renderer.ts --bundle --platform=browser --format=esm --target=es2022 --outfile=dist/renderer/renderer.js --sourcemap",
     "check:main-lines": "bash scripts/check-main-lines.sh",
     "check:main-lines:baseline": "bash scripts/check-main-lines.sh 5300",
     "check:main-lines:gate1": "bash scripts/check-main-lines.sh 4500",
@@ -55,6 +56,7 @@
     "@types/node": "^25.2.2",
     "@types/ws": "^8.18.1",
     "electron": "^37.10.3",
+    "esbuild": "^0.21.5",
     "electron-builder": "^26.7.0",
     "typescript": "^5.9.3",
     "vitepress": "^1.6.3"
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 6b11cf7..0fcfd5f 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -36,6 +36,9 @@ importers:
       electron-builder:
         specifier: ^26.7.0
         version: 26.7.0(electron-builder-squirrel-windows@26.7.0)
+      esbuild:
+        specifier: ^0.21.5
+        version: 0.21.5
       typescript:
         specifier: ^5.9.3
         version: 5.9.3
diff --git a/src/core/services/tokenizer-service.test.ts b/src/core/services/tokenizer-service.test.ts
index 3d1a502..3ce56f1 100644
--- a/src/core/services/tokenizer-service.test.ts
+++ b/src/core/services/tokenizer-service.test.ts
@@ -88,6 +88,108 @@ test("tokenizeSubtitleService assigns JLPT level to parsed Yomitan tokens", asyn
   assert.equal(result.tokens?.[0]?.jlptLevel, "N5");
 });
 
+test("tokenizeSubtitleService caches JLPT lookups across repeated tokens", async () => {
+  let lookupCalls = 0;
+  const result = await tokenizeSubtitleService(
+    "猫猫",
+    makeDepsFromMecabTokenizer(async () => [
+      {
+        word: "猫",
+        partOfSpeech: PartOfSpeech.noun,
+        pos1: "",
+        pos2: "",
+        pos3: "",
+        pos4: "",
+        inflectionType: "",
+        inflectionForm: "",
+        headword: "猫",
+        katakanaReading: "ネコ",
+        pronunciation: "ネコ",
+      },
+      {
+        word: "猫",
+        partOfSpeech: PartOfSpeech.noun,
+        pos1: "",
+        pos2: "",
+        pos3: "",
+        pos4: "",
+        inflectionType: "",
+        inflectionForm: "",
+        headword: "猫",
+        katakanaReading: "ネコ",
+        pronunciation: "ネコ",
+      },
+    ], {
+      getJlptLevel: (text) => {
+        lookupCalls += 1;
+        return text === "猫" ? "N5" : null;
+      },
+    }),
+  );
+
+  assert.equal(result.tokens?.length, 2);
+  assert.equal(lookupCalls, 1);
+  assert.equal(result.tokens?.[0]?.jlptLevel, "N5");
+  assert.equal(result.tokens?.[1]?.jlptLevel, "N5");
+});
+
+test("tokenizeSubtitleService leaves JLPT unset for non-matching tokens", async () => {
+  const result = await tokenizeSubtitleService(
+    "猫",
+    makeDepsFromMecabTokenizer(async () => [
+      {
+        word: "猫",
+        partOfSpeech: PartOfSpeech.noun,
+        pos1: "",
+        pos2: "",
+        pos3: "",
+        pos4: "",
+        inflectionType: "",
+        inflectionForm: "",
+        headword: "猫",
+        katakanaReading: "ネコ",
+        pronunciation: "ネコ",
+      },
+    ], {
+      getJlptLevel: () => null,
+    }),
+  );
+
+  assert.equal(result.tokens?.length, 1);
+  assert.equal(result.tokens?.[0]?.jlptLevel, undefined);
+});
+
+test("tokenizeSubtitleService skips JLPT lookups when disabled", async () => {
+  let lookupCalls = 0;
+  const result = await tokenizeSubtitleService(
+      "猫です",
+      makeDeps({
+      tokenizeWithMecab: async () => [
+        {
+          headword: "猫",
+          surface: "猫",
+          reading: "ネコ",
+          startPos: 0,
+          endPos: 1,
+          partOfSpeech: PartOfSpeech.noun,
+          isMerged: false,
+          isKnown: false,
+          isNPlusOneTarget: false,
+        },
+      ],
+      getJlptLevel: () => {
+        lookupCalls += 1;
+        return "N5";
+      },
+      getJlptEnabled: () => false,
+    }),
+  );
+
+  assert.equal(result.tokens?.length, 1);
+  assert.equal(result.tokens?.[0]?.jlptLevel, undefined);
+  assert.equal(lookupCalls, 0);
+});
+
 test("tokenizeSubtitleService skips JLPT level for excluded demonstratives", async () => {
   const result = await tokenizeSubtitleService(
     "この",