diff --git a/apps/yms/app/src/main/java/org/onosproject/yms/app/ydt/YdtConstants.java b/apps/yms/app/src/main/java/org/onosproject/yms/app/ydt/YdtConstants.java
new file mode 100644
index 0000000..2063093
--- /dev/null
+++ b/apps/yms/app/src/main/java/org/onosproject/yms/app/ydt/YdtConstants.java
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yms.app.ydt;
+
+/**
+ * Represents common constant utility for YANG data tree.
+ */
+final class YdtConstants {
+
+    //No instantiation.
+    private YdtConstants() {
+    }
+
+    /**
+     * Error formatting string for duplicate entries found in ydt.
+     */
+    public static final String FMT_DUP_ENTRY = "Duplicate entry with name %s.";
+
+    /**
+     * Returns the error string by filling the parameters in the given
+     * formatted error string.
+     *
+     * @param fmt    error format string
+     * @param params parameters to be filled in formatted string
+     * @return error string
+     */
+    public static String errorMsg(String fmt, Object... params) {
+        return String.format(fmt, params);
+    }
+}
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