diff --git a/src/mcp/server.ts b/src/mcp/server.ts
index c9c3a84..5eed89c 100644
--- a/src/mcp/server.ts
+++ b/src/mcp/server.ts
@@ -599,16 +599,23 @@ export class N8NDocumentationMCPServer {
    */
   private validateToolParamsBasic(toolName: string, args: any, requiredParams: string[]): void {
     const missing: string[] = [];
-    
+    const invalid: string[] = [];
+
     for (const param of requiredParams) {
       if (!(param in args) || args[param] === undefined || args[param] === null) {
         missing.push(param);
+      } else if (typeof args[param] === 'string' && args[param].trim() === '') {
+        invalid.push(`${param} (empty string)`);
       }
     }
-    
+
     if (missing.length > 0) {
       throw new Error(`Missing required parameters for ${toolName}: ${missing.join(', ')}. Please provide the required parameters to use this tool.`);
     }
+
+    if (invalid.length > 0) {
+      throw new Error(`Invalid parameters for ${toolName}: ${invalid.join(', ')}. String parameters cannot be empty.`);
+    }
   }
 
   /**
diff --git a/src/utils/node-utils.ts b/src/utils/node-utils.ts
index d6a3d3d..f26aba2 100644
--- a/src/utils/node-utils.ts
+++ b/src/utils/node-utils.ts
@@ -32,13 +32,18 @@ export function normalizeNodeType(nodeType: string): string {
 
 /**
  * Gets alternative node type formats to try for lookups
- * 
+ *
  * @param nodeType The original node type
  * @returns Array of alternative formats to try
  */
 export function getNodeTypeAlternatives(nodeType: string): string[] {
+  // Defensive: validate input to prevent TypeError when nodeType is undefined/null/empty
+  if (!nodeType || typeof nodeType !== 'string' || nodeType.trim() === '') {
+    return [];
+  }
+
   const alternatives: string[] = [];
-  
+
   // Add lowercase version
   alternatives.push(nodeType.toLowerCase());
   
diff --git a/tests/unit/utils/node-utils.test.ts b/tests/unit/utils/node-utils.test.ts
new file mode 100644
index 0000000..0fcee8e
--- /dev/null
+++ b/tests/unit/utils/node-utils.test.ts
@@ -0,0 +1,130 @@
+import { describe, it, expect } from 'vitest';
+import { getNodeTypeAlternatives, normalizeNodeType, getWorkflowNodeType } from '../../../src/utils/node-utils';
+
+describe('node-utils', () => {
+  describe('getNodeTypeAlternatives', () => {
+    describe('valid inputs', () => {
+      it('should generate alternatives for standard node type', () => {
+        const alternatives = getNodeTypeAlternatives('nodes-base.httpRequest');
+
+        expect(alternatives).toContain('nodes-base.httprequest');
+        expect(alternatives.length).toBeGreaterThan(0);
+      });
+
+      it('should generate alternatives for langchain node type', () => {
+        const alternatives = getNodeTypeAlternatives('nodes-langchain.agent');
+
+        expect(alternatives).toContain('nodes-langchain.agent');
+        expect(alternatives.length).toBeGreaterThan(0);
+      });
+
+      it('should generate alternatives for bare node name', () => {
+        const alternatives = getNodeTypeAlternatives('webhook');
+
+        expect(alternatives).toContain('nodes-base.webhook');
+        expect(alternatives).toContain('nodes-langchain.webhook');
+      });
+    });
+
+    describe('invalid inputs - defensive validation', () => {
+      it('should return empty array for undefined', () => {
+        const alternatives = getNodeTypeAlternatives(undefined as any);
+
+        expect(alternatives).toEqual([]);
+      });
+
+      it('should return empty array for null', () => {
+        const alternatives = getNodeTypeAlternatives(null as any);
+
+        expect(alternatives).toEqual([]);
+      });
+
+      it('should return empty array for empty string', () => {
+        const alternatives = getNodeTypeAlternatives('');
+
+        expect(alternatives).toEqual([]);
+      });
+
+      it('should return empty array for whitespace-only string', () => {
+        const alternatives = getNodeTypeAlternatives('   ');
+
+        expect(alternatives).toEqual([]);
+      });
+
+      it('should return empty array for non-string input (number)', () => {
+        const alternatives = getNodeTypeAlternatives(123 as any);
+
+        expect(alternatives).toEqual([]);
+      });
+
+      it('should return empty array for non-string input (object)', () => {
+        const alternatives = getNodeTypeAlternatives({} as any);
+
+        expect(alternatives).toEqual([]);
+      });
+
+      it('should return empty array for non-string input (array)', () => {
+        const alternatives = getNodeTypeAlternatives([] as any);
+
+        expect(alternatives).toEqual([]);
+      });
+    });
+
+    describe('edge cases', () => {
+      it('should handle node type with only prefix', () => {
+        const alternatives = getNodeTypeAlternatives('nodes-base.');
+
+        expect(alternatives).toBeInstanceOf(Array);
+      });
+
+      it('should handle node type with multiple dots', () => {
+        const alternatives = getNodeTypeAlternatives('nodes-base.some.complex.type');
+
+        expect(alternatives).toBeInstanceOf(Array);
+        expect(alternatives.length).toBeGreaterThan(0);
+      });
+
+      it('should handle camelCase node names', () => {
+        const alternatives = getNodeTypeAlternatives('nodes-base.httpRequest');
+
+        expect(alternatives).toContain('nodes-base.httprequest');
+      });
+    });
+  });
+
+  describe('normalizeNodeType', () => {
+    it('should normalize n8n-nodes-base prefix', () => {
+      expect(normalizeNodeType('n8n-nodes-base.webhook')).toBe('nodes-base.webhook');
+    });
+
+    it('should normalize @n8n/n8n-nodes-langchain prefix', () => {
+      expect(normalizeNodeType('@n8n/n8n-nodes-langchain.agent')).toBe('nodes-langchain.agent');
+    });
+
+    it('should normalize n8n-nodes-langchain prefix', () => {
+      expect(normalizeNodeType('n8n-nodes-langchain.chatTrigger')).toBe('nodes-langchain.chatTrigger');
+    });
+
+    it('should leave already normalized types unchanged', () => {
+      expect(normalizeNodeType('nodes-base.slack')).toBe('nodes-base.slack');
+    });
+
+    it('should leave community nodes unchanged', () => {
+      expect(normalizeNodeType('community.customNode')).toBe('community.customNode');
+    });
+  });
+
+  describe('getWorkflowNodeType', () => {
+    it('should construct workflow node type for n8n-nodes-base', () => {
+      expect(getWorkflowNodeType('n8n-nodes-base', 'nodes-base.webhook')).toBe('n8n-nodes-base.webhook');
+    });
+
+    it('should construct workflow node type for langchain', () => {
+      expect(getWorkflowNodeType('@n8n/n8n-nodes-langchain', 'nodes-langchain.agent')).toBe('@n8n/n8n-nodes-langchain.agent');
+    });
+
+    it('should return as-is for unknown packages', () => {
+      expect(getWorkflowNodeType('custom-package', 'custom.node')).toBe('custom.node');
+    });
+  });
+});