diff --git a/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/EmojiUrlTag.kt b/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/EmojiUrlTag.kt
index a541d261e..4919ec960 100644
--- a/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/EmojiUrlTag.kt
+++ b/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/EmojiUrlTag.kt
@@ -26,16 +26,27 @@ import androidx.compose.runtime.Immutable
 data class EmojiUrlTag(
     val code: String,
     val url: String,
+    val emojiSet: String? = null,
 ) {
     fun encode(): String = ":$code:$url"
 
     fun toContentEncode(): String = contentEncode(code)
 
-    fun toTagArray() = arrayOf("emoji", code, url)
+    fun toTagArray() =
+        if (emojiSet != null) {
+            arrayOf(TAG_NAME, code, url, emojiSet)
+        } else {
+            arrayOf(TAG_NAME, code, url)
+        }
 
     companion object {
         const val TAG_NAME = "emoji"
 
+        // NIP-30: shortcode MUST be comprised of only alphanumeric characters, hyphens, and underscores.
+        private val SHORTCODE_PATTERN = Regex("^[A-Za-z0-9_\\-]+$")
+
+        fun isValidShortcode(shortcode: String): Boolean = SHORTCODE_PATTERN.matches(shortcode)
+
         fun contentEncode(code: String): String = ":$code:"
 
         fun decode(encodedEmojiSetup: String): EmojiUrlTag? {
@@ -49,7 +60,7 @@ data class EmojiUrlTag(
 
         fun parse(tag: Array<String>): EmojiUrlTag? =
             if (tag.size > 2 && tag[0] == TAG_NAME) {
-                EmojiUrlTag(tag[1], tag[2])
+                EmojiUrlTag(tag[1], tag[2], tag.getOrNull(3))
             } else {
                 null
             }
diff --git a/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/TagArrayBuilderExt.kt b/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/TagArrayBuilderExt.kt
index 0adfe102c..eedccf90c 100644
--- a/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/TagArrayBuilderExt.kt
+++ b/quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/TagArrayBuilderExt.kt
@@ -25,4 +25,10 @@ import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
 
 fun <T : Event> TagArrayBuilder<T>.emoji(tag: EmojiUrlTag) = add(tag.toTagArray())
 
+fun <T : Event> TagArrayBuilder<T>.emoji(
+    code: String,
+    url: String,
+    emojiSet: String? = null,
+) = add(EmojiUrlTag(code, url, emojiSet).toTagArray())
+
 fun <T : Event> TagArrayBuilder<T>.emojis(tags: List<EmojiUrlTag>) = addAll(tags.map { it.toTagArray() })
diff --git a/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/Nip30Test.kt b/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/Nip30Test.kt
index 65ff12631..b76fc651a 100644
--- a/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/Nip30Test.kt
+++ b/quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip30CustomEmoji/Nip30Test.kt
@@ -21,8 +21,11 @@
 package com.vitorpamplona.quartz.nip30CustomEmoji
 
 import kotlin.test.Test
+import kotlin.test.assertContentEquals
 import kotlin.test.assertEquals
+import kotlin.test.assertFalse
 import kotlin.test.assertNull
+import kotlin.test.assertTrue
 
 class Nip30Test {
     @Test()
@@ -164,4 +167,55 @@ class Nip30Test {
         assertEquals("https://media.misskeyusercontent.com/misskey/f6294900-f678-43cc-bc36-3ee5deeca4c2.gif", (result[i++] as CustomEmoji.ImageUrlType).url)
         assertEquals("\u200B\n#ioメシヨソイゲーム\nhttps://misskey.io/play/9g3qza4jow", (result[i] as CustomEmoji.TextType).text)
     }
+
+    @Test
+    fun emojiTagWithoutEmojiSetRoundtrip() {
+        val tag = EmojiUrlTag("soapbox", "http://soapbox")
+        assertContentEquals(arrayOf("emoji", "soapbox", "http://soapbox"), tag.toTagArray())
+        assertEquals(tag, EmojiUrlTag.parse(tag.toTagArray()))
+    }
+
+    @Test
+    fun emojiTagWithEmojiSetRoundtrip() {
+        val setAddress = "30030:abc123:emojis-fall"
+        val tag = EmojiUrlTag("soapbox", "http://soapbox", setAddress)
+        assertContentEquals(arrayOf("emoji", "soapbox", "http://soapbox", setAddress), tag.toTagArray())
+        assertEquals(tag, EmojiUrlTag.parse(tag.toTagArray()))
+    }
+
+    @Test
+    fun parseIgnoresTrailingFields() {
+        val tag = arrayOf("emoji", "soapbox", "http://soapbox", "30030:abc123:pack", "extra")
+        val parsed = EmojiUrlTag.parse(tag)
+        assertEquals(EmojiUrlTag("soapbox", "http://soapbox", "30030:abc123:pack"), parsed)
+    }
+
+    @Test
+    fun parseRejectsWrongTagName() {
+        assertNull(EmojiUrlTag.parse(arrayOf("t", "soapbox", "http://soapbox")))
+    }
+
+    @Test
+    fun parseRejectsTooFewFields() {
+        assertNull(EmojiUrlTag.parse(arrayOf("emoji", "soapbox")))
+    }
+
+    @Test
+    fun validShortcodesAcceptAlphanumericUnderscoreHyphen() {
+        assertTrue(EmojiUrlTag.isValidShortcode("soapbox"))
+        assertTrue(EmojiUrlTag.isValidShortcode("Soap_Box-123"))
+        assertTrue(EmojiUrlTag.isValidShortcode("ABC"))
+        assertTrue(EmojiUrlTag.isValidShortcode("007"))
+    }
+
+    @Test
+    fun invalidShortcodesRejected() {
+        assertFalse(EmojiUrlTag.isValidShortcode(""))
+        assertFalse(EmojiUrlTag.isValidShortcode("soap box"))
+        assertFalse(EmojiUrlTag.isValidShortcode("soap:box"))
+        assertFalse(EmojiUrlTag.isValidShortcode("soap.box"))
+        assertFalse(EmojiUrlTag.isValidShortcode("soap/box"))
+        assertFalse(EmojiUrlTag.isValidShortcode("soap!"))
+        assertFalse(EmojiUrlTag.isValidShortcode("絵文字"))
+    }
 }