diff --git a/nostr-java-api/src/main/java/nostr/config/Constants.java b/nostr-java-api/src/main/java/nostr/config/Constants.java
index 2f3c09812..6777bdbf1 100644
--- a/nostr-java-api/src/main/java/nostr/config/Constants.java
+++ b/nostr-java-api/src/main/java/nostr/config/Constants.java
@@ -1,100 +1,108 @@
+
 package nostr.config;
 
-public interface Constants {
+/**
+ * Collection of common constants used across the API.
+ */
+public final class Constants {
+    private Constants() {
+    }
+
+    public static final class Kind {
+        private Kind() {
+        }
 
-    interface Kind {
-        int USER_METADATA = 0;
-        int SHORT_TEXT_NOTE = 1;
+        public static final int USER_METADATA = 0;
+        public static final int SHORT_TEXT_NOTE = 1;
         @Deprecated
-        int RECOMMENDED_RELAY = 2;
-        int CONTACT_LIST = 3;
-        int ENCRYPTED_DIRECT_MESSAGE = 4;
-        int EVENT_DELETION = 5;
-        int OTS_ATTESTATION = 1040;
-        int DATE_BASED_CALENDAR_CONTENT = 31922;
-        int TIME_BASED_CALENDAR_CONTENT = 31923;
-        int CALENDAR = 31924;
-        int CALENDAR_EVENT_RSVP = 31925;
-        int REPOST = 6;
-        int REACTION = 7;
-        int CHANNEL_CREATION = 40;
-        int CHANNEL_METADATA = 41;
-        int CHANNEL_MESSAGE = 42;
-        int CHANNEL_HIDE_MESSAGE = 43;
-        int CHANNEL_MUTE_USER = 44;
-        int REPORT = 1984;
-        int ZAP_REQUEST = 9734;
-        int ZAP_RECEIPT = 9735;
-        int RELAY_LIST_METADATA = 10002;
-        int CLIENT_AUTHENTICATION = 22242;
-        int BADGE_DEFINITION = 30008;
-        int BADGE_AWARD = 30009;
-        int LONG_FORM_TEXT_NOTE = 30023;
-        int LONG_FORM_DRAFT = 30024;
-        int APPLICATION_SPECIFIC_DATA = 30078;
-        int CASHU_WALLET_EVENT = 17375;
-        int CASHU_WALLET_TOKENS = 7375;
-        int CASHU_WALLET_HISTORY = 7376;
-        int CASHU_RESERVED_WALLET_TOKENS = 7374;
-        int CASHU_NUTZAP_EVENT = 9321;
-        int CASHU_NUTZAP_INFO_EVENT = 10019;
-        int SET_STALL = 30017;
-        int SET_PRODUCT = 30018;
-        int REACTION_TO_WEBSITE = 17;
-        int REQUEST_EVENTS = 24133;
-        int CLASSIFIED_LISTING = 30_402;
-        int RELAY_LIST_METADATA_EVENT = 10_002;
+        public static final int RECOMMENDED_RELAY = 2;
+        public static final int CONTACT_LIST = 3;
+        public static final int ENCRYPTED_DIRECT_MESSAGE = 4;
+        public static final int EVENT_DELETION = 5;
+        public static final int OTS_ATTESTATION = 1040;
+        public static final int DATE_BASED_CALENDAR_CONTENT = 31922;
+        public static final int TIME_BASED_CALENDAR_CONTENT = 31923;
+        public static final int CALENDAR = 31924;
+        public static final int CALENDAR_EVENT_RSVP = 31925;
+        public static final int REPOST = 6;
+        public static final int REACTION = 7;
+        public static final int CHANNEL_CREATION = 40;
+        public static final int CHANNEL_METADATA = 41;
+        public static final int CHANNEL_MESSAGE = 42;
+        public static final int CHANNEL_HIDE_MESSAGE = 43;
+        public static final int CHANNEL_MUTE_USER = 44;
+        public static final int REPORT = 1984;
+        public static final int ZAP_REQUEST = 9734;
+        public static final int ZAP_RECEIPT = 9735;
+        public static final int RELAY_LIST_METADATA = 10002;
+        public static final int CLIENT_AUTHENTICATION = 22242;
+        public static final int BADGE_DEFINITION = 30008;
+        public static final int BADGE_AWARD = 30009;
+        public static final int LONG_FORM_TEXT_NOTE = 30023;
+        public static final int LONG_FORM_DRAFT = 30024;
+        public static final int APPLICATION_SPECIFIC_DATA = 30078;
+        public static final int CASHU_WALLET_EVENT = 17375;
+        public static final int CASHU_WALLET_TOKENS = 7375;
+        public static final int CASHU_WALLET_HISTORY = 7376;
+        public static final int CASHU_RESERVED_WALLET_TOKENS = 7374;
+        public static final int CASHU_NUTZAP_EVENT = 9321;
+        public static final int CASHU_NUTZAP_INFO_EVENT = 10019;
+        public static final int SET_STALL = 30017;
+        public static final int SET_PRODUCT = 30018;
+        public static final int REACTION_TO_WEBSITE = 17;
+        public static final int REQUEST_EVENTS = 24133;
+        public static final int CLASSIFIED_LISTING = 30_402;
+        public static final int RELAY_LIST_METADATA_EVENT = 10_002;
     }
 
-    interface Tag {
-        String EVENT_CODE = "e";
-        String PUBKEY_CODE = "p";
-        String IDENTITY_CODE = "d";
-        String ADDRESS_CODE = "a";
-        String HASHTAG_CODE = "t";
-        String REFERENCE_CODE = "r";
-        String GEOHASH_CODE = "g";
-        String SUBJECT_CODE = "subject";
-        String TITLE_CODE = "title";
-        String IMAGE_CODE = "image";
-        String PUBLISHED_AT_CODE = "published_at";
-        String SUMMARY_CODE = "summary";
-        String KIND_CODE = "k";
-        String EMOJI_CODE = "emoji";
-        String ALT_CODE = "alt";
-        String NAMESPACE_CODE = "L";
-        String LABEL_CODE = "l";
-        String EXPIRATION_CODE = "expiration";
-        String RELAY_CODE = "relay";
-        String RELAYS_CODE = "relays";
-        String CHALLENGE_CODE = "challenge";
-        String AMOUNT_CODE = "amount";
-        String LNURL_CODE = "lnurl";
-        String BOLT11_CODE = "bolt11";
-        String PREIMAGE_CODE = "preimage";
-        String DESCRIPTION_CODE = "description";
-        String ZAP_CODE = "zap";
-        String RECIPIENT_PUBKEY_CODE = "P";
-        String MINT_CODE = "mint";
-        String UNIT_CODE = "unit";
-        String PRIVKEY_CODE = "privkey";
-        String BALANCE_CODE = "balance";
-        String DIRECTION_CODE = "direction";
-        String P2PKH_CODE = "pubkey";
-        String URL_CODE = "u";
-        String PROOF_CODE = "proof";
-        String LOCATION_CODE = "location";
-        String PRICE_CODE = "price";
-        String STATUS_CODE = "status";
-        String START_CODE = "start";
-        String END_CODE = "end";
-        String START_TZID_CODE = "start_tzid";
-        String END_TZID_CODE = "end_tzid";
-        String FREE_BUSY_CODE = "fb";
-    }
+    public static final class Tag {
+        private Tag() {
+        }
 
-    interface NIP {
-        int ONE = 1;
-        int TWO = 2;
+        public static final String EVENT_CODE = "e";
+        public static final String PUBKEY_CODE = "p";
+        public static final String IDENTITY_CODE = "d";
+        public static final String ADDRESS_CODE = "a";
+        public static final String HASHTAG_CODE = "t";
+        public static final String REFERENCE_CODE = "r";
+        public static final String GEOHASH_CODE = "g";
+        public static final String SUBJECT_CODE = "subject";
+        public static final String TITLE_CODE = "title";
+        public static final String IMAGE_CODE = "image";
+        public static final String PUBLISHED_AT_CODE = "published_at";
+        public static final String SUMMARY_CODE = "summary";
+        public static final String KIND_CODE = "k";
+        public static final String EMOJI_CODE = "emoji";
+        public static final String ALT_CODE = "alt";
+        public static final String NAMESPACE_CODE = "L";
+        public static final String LABEL_CODE = "l";
+        public static final String EXPIRATION_CODE = "expiration";
+        public static final String RELAY_CODE = "relay";
+        public static final String RELAYS_CODE = "relays";
+        public static final String CHALLENGE_CODE = "challenge";
+        public static final String AMOUNT_CODE = "amount";
+        public static final String LNURL_CODE = "lnurl";
+        public static final String BOLT11_CODE = "bolt11";
+        public static final String PREIMAGE_CODE = "preimage";
+        public static final String DESCRIPTION_CODE = "description";
+        public static final String ZAP_CODE = "zap";
+        public static final String RECIPIENT_PUBKEY_CODE = "P";
+        public static final String MINT_CODE = "mint";
+        public static final String UNIT_CODE = "unit";
+        public static final String PRIVKEY_CODE = "privkey";
+        public static final String BALANCE_CODE = "balance";
+        public static final String DIRECTION_CODE = "direction";
+        public static final String P2PKH_CODE = "pubkey";
+        public static final String URL_CODE = "u";
+        public static final String PROOF_CODE = "proof";
+        public static final String LOCATION_CODE = "location";
+        public static final String PRICE_CODE = "price";
+        public static final String STATUS_CODE = "status";
+        public static final String START_CODE = "start";
+        public static final String END_CODE = "end";
+        public static final String START_TZID_CODE = "start_tzid";
+        public static final String END_TZID_CODE = "end_tzid";
+        public static final String FREE_BUSY_CODE = "fb";
     }
+
 }
\ No newline at end of file
diff --git a/nostr-java-api/src/test/java/nostr/api/unit/ConstantsTest.java b/nostr-java-api/src/test/java/nostr/api/unit/ConstantsTest.java
new file mode 100644
index 000000000..31d7e1d0f
--- /dev/null
+++ b/nostr-java-api/src/test/java/nostr/api/unit/ConstantsTest.java
@@ -0,0 +1,40 @@
+package nostr.api.unit;
+
+import nostr.config.Constants;
+import nostr.event.impl.GenericEvent;
+import nostr.event.json.codec.BaseEventEncoder;
+import nostr.id.Identity;
+import org.junit.jupiter.api.Test;
+
+import static nostr.base.IEvent.MAPPER_AFTERBURNER;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ConstantsTest {
+
+    @Test
+    void testKindValues() {
+        assertEquals(0, Constants.Kind.USER_METADATA);
+        assertEquals(1, Constants.Kind.SHORT_TEXT_NOTE);
+        assertEquals(42, Constants.Kind.CHANNEL_MESSAGE);
+    }
+
+    @Test
+    void testTagValues() {
+        assertEquals("e", Constants.Tag.EVENT_CODE);
+        assertEquals("p", Constants.Tag.PUBKEY_CODE);
+    }
+
+    @Test
+    void testSerializationWithConstants() throws Exception {
+        Identity identity = Identity.generateRandomIdentity();
+        GenericEvent event = new GenericEvent();
+        event.setKind(Constants.Kind.SHORT_TEXT_NOTE);
+        event.setPubKey(identity.getPublicKey());
+        event.setCreatedAt(0L);
+        event.setContent("test");
+
+        String json = new BaseEventEncoder<>(event).encode();
+        assertEquals(Constants.Kind.SHORT_TEXT_NOTE,
+                MAPPER_AFTERBURNER.readTree(json).get("kind").asInt());
+    }
+}