diff --git a/package-lock.json b/package-lock.json
index 1cba085..52578e2 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -13,7 +13,7 @@
         "axios": "^1.7.0",
         "form-data": "^4.0.5",
         "md-to-adf": "^0.5.0",
-        "zod": "^3.22.4"
+        "zod": "^4.4.2"
       },
       "bin": {
         "mcp-jira-stdio": "dist/index.js"
@@ -5136,9 +5136,9 @@
       }
     },
     "node_modules/zod": {
-      "version": "3.25.76",
-      "resolved": "https://registry.npmjs.org/zod/-/zod-3.25.76.tgz",
-      "integrity": "sha512-gzUt/qt81nXsFGKIFcC3YnfEAx5NkunCfnDlvuBSSFS02bcXu4Lmea0AFIUwbLWxWPx3d9p8S5QoaujKcNQxcQ==",
+      "version": "4.4.2",
+      "resolved": "https://registry.npmjs.org/zod/-/zod-4.4.2.tgz",
+      "integrity": "sha512-IynmDyxsEsb9RKzO3J9+4SxXnl2FTFSzNBaKKaMV6tsSk0rw9gYw9gs+JFCq/qk2LCZ78KDwyj+Z289TijSkUw==",
       "license": "MIT",
       "funding": {
         "url": "https://github.com/sponsors/colinhacks"
diff --git a/package.json b/package.json
index 2f08b18..a7164b0 100644
--- a/package.json
+++ b/package.json
@@ -53,7 +53,7 @@
     "axios": "^1.7.0",
     "form-data": "^4.0.5",
     "md-to-adf": "^0.5.0",
-    "zod": "^3.22.4"
+    "zod": "^4.4.2"
   },
   "devDependencies": {
     "@types/node": "^25.3.3",
diff --git a/src/types/tools.ts b/src/types/tools.ts
index 4d505b9..31d211e 100644
--- a/src/types/tools.ts
+++ b/src/types/tools.ts
@@ -61,7 +61,7 @@ export const CreateIssueInputSchema = z.object({
   labels: z.array(z.string()).optional().describe('Issue labels'),
   components: z.array(z.string()).optional().describe('Component names'),
   customFields: z
-    .record(z.any())
+    .record(z.string(), z.any())
     .optional()
     .describe(
       'Additional Jira field mappings, e.g. { "customfield_12345": value }. Use for required custom fields.'
diff --git a/src/utils/validators.ts b/src/utils/validators.ts
index 8b1ac90..7c22dc9 100644
--- a/src/utils/validators.ts
+++ b/src/utils/validators.ts
@@ -6,7 +6,7 @@ export function validateInput<T>(schema: ZodSchema<T>, input: unknown): T {
     return schema.parse(input);
   } catch (error) {
     if (error instanceof z.ZodError) {
-      const errorMessages = error.errors.map((err) => `${err.path.join('.')}: ${err.message}`);
+      const errorMessages = error.issues.map((err) => `${err.path.join('.')}: ${err.message}`);
       throw new Error(`${ERROR_MESSAGES.VALIDATION_ERROR}\n${errorMessages.join('\n')}`);
     }
     throw error;
diff --git a/tests/unit/tools/create-issue-link.test.ts b/tests/unit/tools/create-issue-link.test.ts
index 8de338c..1880d4f 100644
--- a/tests/unit/tools/create-issue-link.test.ts
+++ b/tests/unit/tools/create-issue-link.test.ts
@@ -4,6 +4,7 @@ import {
   createIssueLinkTool,
 } from '../../../src/tools/create-issue-link.js';
 import { validateInput } from '../../../src/utils/validators.js';
+import { CreateIssueLinkInputSchema } from '../../../src/types/tools.js';
 import { createIssueLink } from '../../../src/utils/api-helpers.js';
 import { formatSuccessResponse } from '../../../src/utils/formatters.js';
 import { handleError } from '../../../src/utils/error-handler.js';
@@ -194,14 +195,7 @@ describe('create-issue-link tool', () => {
 
         await handleCreateIssueLink(input);
 
-        expect(mockedValidateInput).toHaveBeenCalledWith(
-          expect.objectContaining({
-            _def: expect.objectContaining({
-              typeName: 'ZodObject',
-            }),
-          }),
-          input
-        );
+        expect(mockedValidateInput).toHaveBeenCalledWith(CreateIssueLinkInputSchema, input);
       });
 
       it('should handle validation errors for missing fromIssue', async () => {
diff --git a/tests/unit/tools/create-issue.test.ts b/tests/unit/tools/create-issue.test.ts
index cc5639d..504833a 100644
--- a/tests/unit/tools/create-issue.test.ts
+++ b/tests/unit/tools/create-issue.test.ts
@@ -1,6 +1,7 @@
 import { describe, it, expect, beforeEach, vi } from 'vitest';
 import { handleCreateIssue, createIssueTool } from '../../../src/tools/create-issue.js';
 import { validateInput } from '../../../src/utils/validators.js';
+import { CreateIssueInputSchema } from '../../../src/types/tools.js';
 import { createIssue } from '../../../src/utils/api-helpers.js';
 import { formatIssueResponse } from '../../../src/utils/formatters.js';
 import { handleError } from '../../../src/utils/error-handler.js';
@@ -219,14 +220,7 @@ describe('create-issue tool', () => {
 
         await handleCreateIssue(input);
 
-        expect(mockedValidateInput).toHaveBeenCalledWith(
-          expect.objectContaining({
-            _def: expect.objectContaining({
-              typeName: 'ZodObject',
-            }),
-          }),
-          input
-        );
+        expect(mockedValidateInput).toHaveBeenCalledWith(CreateIssueInputSchema, input);
       });
 
       it('should handle validation errors for missing required fields', async () => {
diff --git a/tests/unit/tools/get-issue.test.ts b/tests/unit/tools/get-issue.test.ts
index 26f6fc9..e628196 100644
--- a/tests/unit/tools/get-issue.test.ts
+++ b/tests/unit/tools/get-issue.test.ts
@@ -1,6 +1,7 @@
 import { describe, it, expect, beforeEach, vi } from 'vitest';
 import { handleGetIssue, getIssueTool } from '../../../src/tools/get-issue.js';
 import { validateInput, extractIssueKey } from '../../../src/utils/validators.js';
+import { GetIssueInputSchema } from '../../../src/types/tools.js';
 import { getIssue } from '../../../src/utils/api-helpers.js';
 import { formatIssueResponse } from '../../../src/utils/formatters.js';
 import { handleError } from '../../../src/utils/error-handler.js';
@@ -201,14 +202,7 @@ describe('get-issue tool', () => {
 
         await handleGetIssue(input);
 
-        expect(mockedValidateInput).toHaveBeenCalledWith(
-          expect.objectContaining({
-            _def: expect.objectContaining({
-              typeName: 'ZodObject',
-            }),
-          }),
-          input
-        );
+        expect(mockedValidateInput).toHaveBeenCalledWith(GetIssueInputSchema, input);
       });
 
       it('should handle validation errors', async () => {
diff --git a/tests/unit/tools/search-issues.test.ts b/tests/unit/tools/search-issues.test.ts
index 11c83ca..288e9de 100644
--- a/tests/unit/tools/search-issues.test.ts
+++ b/tests/unit/tools/search-issues.test.ts
@@ -1,6 +1,7 @@
 import { describe, it, expect, beforeEach, vi } from 'vitest';
 import { handleSearchIssues, searchIssuesTool } from '../../../src/tools/search-issues.js';
 import { validateInput } from '../../../src/utils/validators.js';
+import { SearchIssuesInputSchema } from '../../../src/types/tools.js';
 import { searchIssues } from '../../../src/utils/api-helpers.js';
 import { formatSearchResultsResponse } from '../../../src/utils/formatters.js';
 import { handleError } from '../../../src/utils/error-handler.js';
@@ -207,14 +208,7 @@ describe('search-issues tool', () => {
 
         await handleSearchIssues(input);
 
-        expect(mockedValidateInput).toHaveBeenCalledWith(
-          expect.objectContaining({
-            _def: expect.objectContaining({
-              typeName: 'ZodObject',
-            }),
-          }),
-          input
-        );
+        expect(mockedValidateInput).toHaveBeenCalledWith(SearchIssuesInputSchema, input);
       });
 
       it('should handle validation errors for missing JQL', async () => {
diff --git a/tests/unit/utils/validators.test.ts b/tests/unit/utils/validators.test.ts
index b47db45..f4bb1c6 100644
--- a/tests/unit/utils/validators.test.ts
+++ b/tests/unit/utils/validators.test.ts
@@ -37,8 +37,8 @@ describe('validators', () => {
 
     it('should handle missing required fields', () => {
       const input = { age: 30 };
-      expect(() => validateInput(testSchema, input)).toThrow('name: Required');
-      expect(() => validateInput(testSchema, input)).toThrow('email: Required');
+      expect(() => validateInput(testSchema, input)).toThrow('name: Invalid input');
+      expect(() => validateInput(testSchema, input)).toThrow('email: Invalid input');
     });
 
     it('should rethrow non-zod errors', () => {