diff --git a/src/types.test.ts b/src/types.test.ts
index 3f6f83a14..e6ea0b6d6 100644
--- a/src/types.test.ts
+++ b/src/types.test.ts
@@ -6,6 +6,7 @@ import {
     PromptMessageSchema,
     CallToolResultSchema,
     CompleteRequestSchema,
+    ToolSchema,
     ToolUseContentSchema,
     ToolResultContentSchema,
     ToolChoiceSchema,
@@ -319,6 +320,132 @@ describe('Types', () => {
         });
     });
 
+    describe('ToolSchema - JSON Schema 2020-12 support', () => {
+        test('should accept inputSchema with $schema field', () => {
+            const tool = {
+                name: 'test',
+                inputSchema: {
+                    $schema: 'https://json-schema.org/draft/2020-12/schema',
+                    type: 'object',
+                    properties: { name: { type: 'string' } }
+                }
+            };
+            const result = ToolSchema.safeParse(tool);
+            expect(result.success).toBe(true);
+        });
+
+        test('should accept inputSchema with additionalProperties', () => {
+            const tool = {
+                name: 'test',
+                inputSchema: {
+                    type: 'object',
+                    properties: { name: { type: 'string' } },
+                    additionalProperties: false
+                }
+            };
+            const result = ToolSchema.safeParse(tool);
+            expect(result.success).toBe(true);
+        });
+
+        test('should accept inputSchema with composition keywords', () => {
+            const tool = {
+                name: 'test',
+                inputSchema: {
+                    type: 'object',
+                    allOf: [{ properties: { a: { type: 'string' } } }, { properties: { b: { type: 'number' } } }]
+                }
+            };
+            const result = ToolSchema.safeParse(tool);
+            expect(result.success).toBe(true);
+        });
+
+        test('should accept inputSchema with $ref and $defs', () => {
+            const tool = {
+                name: 'test',
+                inputSchema: {
+                    type: 'object',
+                    properties: { user: { $ref: '#/$defs/User' } },
+                    $defs: {
+                        User: { type: 'object', properties: { name: { type: 'string' } } }
+                    }
+                }
+            };
+            const result = ToolSchema.safeParse(tool);
+            expect(result.success).toBe(true);
+        });
+
+        test('should accept inputSchema with metadata keywords', () => {
+            const tool = {
+                name: 'test',
+                inputSchema: {
+                    type: 'object',
+                    title: 'User Input',
+                    description: 'Input parameters for user creation',
+                    deprecated: false,
+                    examples: [{ name: 'John' }],
+                    properties: { name: { type: 'string' } }
+                }
+            };
+            const result = ToolSchema.safeParse(tool);
+            expect(result.success).toBe(true);
+        });
+
+        test('should accept outputSchema with full JSON Schema features', () => {
+            const tool = {
+                name: 'test',
+                inputSchema: { type: 'object' },
+                outputSchema: {
+                    type: 'object',
+                    properties: {
+                        id: { type: 'string' },
+                        tags: { type: 'array' }
+                    },
+                    required: ['id'],
+                    additionalProperties: false,
+                    minProperties: 1
+                }
+            };
+            const result = ToolSchema.safeParse(tool);
+            expect(result.success).toBe(true);
+        });
+
+        test('should still require type: object at root for inputSchema', () => {
+            const tool = {
+                name: 'test',
+                inputSchema: {
+                    type: 'string'
+                }
+            };
+            const result = ToolSchema.safeParse(tool);
+            expect(result.success).toBe(false);
+        });
+
+        test('should still require type: object at root for outputSchema', () => {
+            const tool = {
+                name: 'test',
+                inputSchema: { type: 'object' },
+                outputSchema: {
+                    type: 'array'
+                }
+            };
+            const result = ToolSchema.safeParse(tool);
+            expect(result.success).toBe(false);
+        });
+
+        test('should accept simple minimal schema (backward compatibility)', () => {
+            const tool = {
+                name: 'test',
+                inputSchema: {
+                    type: 'object',
+                    properties: { name: { type: 'string' } },
+                    required: ['name']
+                }
+            };
+            const result = ToolSchema.safeParse(tool);
+            expect(result.success).toBe(true);
+        });
+    });
+
     describe('ToolUseContent', () => {
         test('should validate a tool call content', () => {
             const toolCall = {
diff --git a/src/types.ts b/src/types.ts
index 64153094d..4ff815ceb 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -999,24 +999,28 @@ export const ToolSchema = z.object({
      */
     description: z.string().optional(),
     /**
-     * A JSON Schema object defining the expected parameters for the tool.
+     * A JSON Schema 2020-12 object defining the expected parameters for the tool.
+     * Must have type: 'object' at the root level per MCP spec.
      */
-    inputSchema: z.object({
-        type: z.literal('object'),
-        properties: z.record(z.string(), AssertObjectSchema).optional(),
-        required: z.optional(z.array(z.string()))
-    }),
+    inputSchema: z
+        .object({
+            type: z.literal('object'),
+            properties: z.record(z.string(), AssertObjectSchema).optional(),
+            required: z.array(z.string()).optional()
+        })
+        .catchall(z.unknown()),
     /**
-     * An optional JSON Schema object defining the structure of the tool's output returned in
-     * the structuredContent field of a CallToolResult.
+     * An optional JSON Schema 2020-12 object defining the structure of the tool's output
+     * returned in the structuredContent field of a CallToolResult.
+     * Must have type: 'object' at the root level per MCP spec.
      */
     outputSchema: z
         .object({
             type: z.literal('object'),
             properties: z.record(z.string(), AssertObjectSchema).optional(),
-            required: z.optional(z.array(z.string())),
-            additionalProperties: z.optional(z.boolean())
+            required: z.array(z.string()).optional()
         })
+        .catchall(z.unknown())
         .optional(),
     /**
      * Optional additional tool information.
diff --git a/src/validation/cfworker-provider.ts b/src/validation/cfworker-provider.ts
index 60ec3f06e..adb102037 100644
--- a/src/validation/cfworker-provider.ts
+++ b/src/validation/cfworker-provider.ts
@@ -4,7 +4,6 @@
  * This provider uses @cfworker/json-schema for validation without code generation,
  * making it compatible with edge runtimes like Cloudflare Workers that restrict
  * eval and new Function.
- *
  */
 
 import { type Schema, Validator } from '@cfworker/json-schema';