diff --git a/web-app/django/VIM/apps/instruments/utils/validators.py b/web-app/django/VIM/apps/instruments/utils/validators.py
index ec960f89..130e4685 100644
--- a/web-app/django/VIM/apps/instruments/utils/validators.py
+++ b/web-app/django/VIM/apps/instruments/utils/validators.py
@@ -135,9 +135,9 @@ def validate_hbs_classification(hbs_class: str) -> bool:
     Validate Hornbostel-Sachs classification format.
 
     Valid formats:
-    - Two digits minimum (e.g., "11", "21")
-    - With optional sub-classifications (e.g., "21.2", "311.121")
-    - First digit must be 1-5, second digit 0-9
+    - At least 1 character, only digits (1-9), dot, dash, and plus permitted
+    - First character must be 1-5
+    - If there is a second character, it must be 1-5
 
     Args:
         hbs_class: Hornbostel-Sachs classification string to validate
@@ -147,16 +147,25 @@ def validate_hbs_classification(hbs_class: str) -> bool:
 
     Example:
         >>> validate_hbs_classification("11")       # True
-        >>> validate_hbs_classification("21.2")     # True
-        >>> validate_hbs_classification("311.121")  # True
-        >>> validate_hbs_classification("6")        # False (needs 2 digits)
-        >>> validate_hbs_classification("11x")      # False (invalid format)
+        >>> validate_hbs_classification("21.2+2")   # True
+        >>> validate_hbs_classification("6")        # False (first char not 1-5)
+        >>> validate_hbs_classification("11x")      # False (invalid char)
     """
     if not hbs_class:
         return False
-    # Pattern: one digit (1-5), followed by another digit, optionally followed by more .digits
-    pattern = r"^[1-5][0-9](\.[0-9]+)*$"
-    return bool(re.match(pattern, hbs_class)) and len(hbs_class) >= 2
+        # Only digits (1-9), dot, dash, plus permitted
+    if not re.match(r"^[1-9.\-+]+$", hbs_class):
+        return False
+    # First character must be 1-5
+    first_char = hbs_class[0]
+    if not re.match(r"[1-5]", first_char):
+        return False
+    # If there is a second character, it must be 1-5
+    if len(hbs_class) > 1:
+        second_char = hbs_class[1]
+        if not re.match(r"[1-5]", second_char):
+            return False
+    return True
 
 
 def validate_image_file(image_file) -> Tuple[bool, str]:
diff --git a/web-app/frontend/src/instruments/helpers/CreateInstrumentValidator.ts b/web-app/frontend/src/instruments/helpers/CreateInstrumentValidator.ts
index 497580a4..6534562b 100644
--- a/web-app/frontend/src/instruments/helpers/CreateInstrumentValidator.ts
+++ b/web-app/frontend/src/instruments/helpers/CreateInstrumentValidator.ts
@@ -1,5 +1,6 @@
 import { WikidataLanguage, ValidationResult, NameEntry } from '../Types';
 import { DatabaseService } from './DatabaseService';
+import { isValidHBSClass } from './NameValidator';
 
 export interface CreateInstrumentData {
   entries: NameEntry[];
@@ -41,13 +42,11 @@ export class CreateInstrumentValidator {
       };
     }
 
-    // Pattern: starts with 1-5, followed by another digit, optionally more .digits
-    const pattern = /^[1-5][0-9](\.[0-9]+)*$/;
-    if (!pattern.test(value.trim())) {
+    if (!isValidHBSClass(value.trim())) {
       return {
         isValid: false,
         message:
-          'Invalid format. Enter at least 2 digits (e.g., "11", "21.2", "311.121")',
+          'Invalid format. Enter a valid HBS class (e.g., "11", "21.2", "311.121"). Must start with 1-5; only digits, dot, dash, and plus are permitted',
         type: 'error',
       };
     }
diff --git a/web-app/frontend/src/instruments/helpers/NameValidator.ts b/web-app/frontend/src/instruments/helpers/NameValidator.ts
index 7a81e3c3..88e9e6d1 100644
--- a/web-app/frontend/src/instruments/helpers/NameValidator.ts
+++ b/web-app/frontend/src/instruments/helpers/NameValidator.ts
@@ -1,6 +1,21 @@
 import { WikidataLanguage, ValidationResult } from '../Types';
 import { WikidataService } from './WikidataService';
 
+// Helper function to validate HBS class input
+export function isValidHBSClass(input: string): boolean {
+  // Only allow digits, dot, dash, and plus
+  if (!/^[1-9.\-+]+$/.test(input)) return false;
+  // The first and second characters must be a digit between 1 and 5
+  if (input.length < 1) return false;
+  const firstChar = input.charAt(0);
+  if (!/[1-5]/.test(firstChar)) return false;
+  if (input.length > 1) {
+    const secondChar = input.charAt(1);
+    if (!/[1-5]/.test(secondChar)) return false;
+  }
+  return true;
+}
+
 export class NameValidator {
   private languages: WikidataLanguage[];
 
@@ -91,6 +106,40 @@ export class NameValidator {
     };
   }
 
+  /**
+   * Validates Hornbostel-Sachs class input (for Add Class form)
+   */
+  validateHBSClassInput(hbsClassInput: string): ValidationResult {
+    const input = hbsClassInput?.trim();
+    if (!input) {
+      return {
+        isValid: false,
+        message: 'Please input an HBS number.',
+        type: 'error',
+      };
+    }
+    if (input.length > 50) {
+      return {
+        isValid: false,
+        message: 'HBS number must be at most 50 characters.',
+        type: 'error',
+      };
+    }
+    if (!isValidHBSClass(input)) {
+      return {
+        isValid: false,
+        message:
+          'Only use digits (first two characters 1–5), and the symbols ".", "-", "+".',
+        type: 'error',
+      };
+    }
+    return {
+      isValid: true,
+      message: `Proposed Classification: ${input}`,
+      type: 'success',
+    };
+  }
+
   /**
    * Validates that we have a valid name ID for deletion
    */