diff --git a/src/main/kotlin/com/florexlabs/docscribe/annotator/DocscribeAnnotator.kt b/src/main/kotlin/com/florexlabs/docscribe/annotator/DocscribeAnnotator.kt
index f662511..8211d7e 100644
--- a/src/main/kotlin/com/florexlabs/docscribe/annotator/DocscribeAnnotator.kt
+++ b/src/main/kotlin/com/florexlabs/docscribe/annotator/DocscribeAnnotator.kt
@@ -417,6 +417,9 @@ class DocscribeAnnotator : ExternalAnnotator<AnnotatorFileInfo, DocscribeOutput>
         project: Project,
         projectDir: String,
     ) {
+        val now = System.currentTimeMillis()
+        if (!shouldShowGemBalloon(lastGemBalloonShown[projectDir], now)) return
+        lastGemBalloonShown[projectDir] = now
         try {
             val group =
                 com.intellij.notification.NotificationGroupManager
@@ -524,6 +527,31 @@ class DocscribeAnnotator : ExternalAnnotator<AnnotatorFileInfo, DocscribeOutput>
     companion object {
         private const val MAX_STDERR_PREVIEW = 200
 
+        /**
+         * Minimum interval between "gem not installed" balloons per project directory.
+         * Prevents spamming the user on every opened file when the gem is missing.
+         */
+        const val BALLOON_THROTTLE_MS = 15 * 60 * 1000L
+
+        /**
+         * Last shown timestamp of the "gem not installed" balloon per project directory.
+         */
+        @VisibleForTesting
+        internal val lastGemBalloonShown = ConcurrentHashMap<String, Long>()
+
+        /**
+         * Whether the "gem not installed" balloon may be shown now.
+         *
+         * @param lastShownMs Previous show timestamp, or `null` if never shown.
+         * @param nowMs Current time in milliseconds.
+         * @return `true` on first show or when [BALLOON_THROTTLE_MS] elapsed.
+         */
+        @JvmStatic
+        fun shouldShowGemBalloon(
+            lastShownMs: Long?,
+            nowMs: Long = System.currentTimeMillis(),
+        ): Boolean = lastShownMs == null || nowMs - lastShownMs >= BALLOON_THROTTLE_MS
+
         /**
          * Generation counter per file path.
          *
diff --git a/src/test/kotlin/com/florexlabs/docscribe/annotator/DocscribeAnnotatorBalloonThrottleTest.kt b/src/test/kotlin/com/florexlabs/docscribe/annotator/DocscribeAnnotatorBalloonThrottleTest.kt
new file mode 100644
index 0000000..4f73dfd
--- /dev/null
+++ b/src/test/kotlin/com/florexlabs/docscribe/annotator/DocscribeAnnotatorBalloonThrottleTest.kt
@@ -0,0 +1,39 @@
+package com.florexlabs.docscribe.annotator
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+class DocscribeAnnotatorBalloonThrottleTest {
+    @Test
+    fun `throttle interval is 15 minutes`() {
+        assertEquals(15 * 60 * 1000L, DocscribeAnnotator.BALLOON_THROTTLE_MS)
+    }
+
+    @Test
+    fun `first show is allowed`() {
+        assertTrue(DocscribeAnnotator.shouldShowGemBalloon(null, 1_000L))
+    }
+
+    @Test
+    fun `repeat within window is suppressed`() {
+        val now = 1_000_000L
+        assertFalse(DocscribeAnnotator.shouldShowGemBalloon(now, now))
+        assertFalse(DocscribeAnnotator.shouldShowGemBalloon(now - 1_000L, now))
+        assertFalse(DocscribeAnnotator.shouldShowGemBalloon(now - DocscribeAnnotator.BALLOON_THROTTLE_MS + 1, now))
+    }
+
+    @Test
+    fun `show allowed exactly at boundary`() {
+        val now = 1_000_000L
+        assertTrue(DocscribeAnnotator.shouldShowGemBalloon(now - DocscribeAnnotator.BALLOON_THROTTLE_MS, now))
+    }
+
+    @Test
+    fun `show allowed after window elapsed`() {
+        val now = 1_000_000L
+        assertTrue(DocscribeAnnotator.shouldShowGemBalloon(now - DocscribeAnnotator.BALLOON_THROTTLE_MS - 1, now))
+        assertTrue(DocscribeAnnotator.shouldShowGemBalloon(0L, now))
+    }
+}