diff --git a/packages/core/src/types/schemas.ts b/packages/core/src/types/schemas.ts
index 86acf11d7..a8a6a66f3 100644
--- a/packages/core/src/types/schemas.ts
+++ b/packages/core/src/types/schemas.ts
@@ -1717,77 +1717,89 @@ export const CreateMessageResultWithToolsSchema = ResultSchema.extend({
 /**
  * Primitive schema definition for boolean fields.
  */
-export const BooleanSchemaSchema = z.object({
-    type: z.literal('boolean'),
-    title: z.string().optional(),
-    description: z.string().optional(),
-    default: z.boolean().optional()
-});
+export const BooleanSchemaSchema = z
+    .object({
+        type: z.literal('boolean'),
+        title: z.string().optional(),
+        description: z.string().optional(),
+        default: z.boolean().optional()
+    })
+    .passthrough();
 
 /**
  * Primitive schema definition for string fields.
  */
-export const StringSchemaSchema = z.object({
-    type: z.literal('string'),
-    title: z.string().optional(),
-    description: z.string().optional(),
-    minLength: z.number().optional(),
-    maxLength: z.number().optional(),
-    format: z.enum(['email', 'uri', 'date', 'date-time']).optional(),
-    default: z.string().optional()
-});
+export const StringSchemaSchema = z
+    .object({
+        type: z.literal('string'),
+        title: z.string().optional(),
+        description: z.string().optional(),
+        minLength: z.number().optional(),
+        maxLength: z.number().optional(),
+        format: z.enum(['email', 'uri', 'date', 'date-time']).optional(),
+        default: z.string().optional()
+    })
+    .passthrough();
 
 /**
  * Primitive schema definition for number fields.
  */
-export const NumberSchemaSchema = z.object({
-    type: z.enum(['number', 'integer']),
-    title: z.string().optional(),
-    description: z.string().optional(),
-    minimum: z.number().optional(),
-    maximum: z.number().optional(),
-    default: z.number().optional()
-});
+export const NumberSchemaSchema = z
+    .object({
+        type: z.enum(['number', 'integer']),
+        title: z.string().optional(),
+        description: z.string().optional(),
+        minimum: z.number().optional(),
+        maximum: z.number().optional(),
+        default: z.number().optional()
+    })
+    .passthrough();
 
 /**
  * Schema for single-selection enumeration without display titles for options.
  */
-export const UntitledSingleSelectEnumSchemaSchema = z.object({
-    type: z.literal('string'),
-    title: z.string().optional(),
-    description: z.string().optional(),
-    enum: z.array(z.string()),
-    default: z.string().optional()
-});
+export const UntitledSingleSelectEnumSchemaSchema = z
+    .object({
+        type: z.literal('string'),
+        title: z.string().optional(),
+        description: z.string().optional(),
+        enum: z.array(z.string()),
+        default: z.string().optional()
+    })
+    .passthrough();
 
 /**
  * Schema for single-selection enumeration with display titles for each option.
  */
-export const TitledSingleSelectEnumSchemaSchema = z.object({
-    type: z.literal('string'),
-    title: z.string().optional(),
-    description: z.string().optional(),
-    oneOf: z.array(
-        z.object({
-            const: z.string(),
-            title: z.string()
-        })
-    ),
-    default: z.string().optional()
-});
+export const TitledSingleSelectEnumSchemaSchema = z
+    .object({
+        type: z.literal('string'),
+        title: z.string().optional(),
+        description: z.string().optional(),
+        oneOf: z.array(
+            z.object({
+                const: z.string(),
+                title: z.string()
+            })
+        ),
+        default: z.string().optional()
+    })
+    .passthrough();
 
 /**
  * Use {@linkcode TitledSingleSelectEnumSchema} instead.
  * This interface will be removed in a future version.
  */
-export const LegacyTitledEnumSchemaSchema = z.object({
-    type: z.literal('string'),
-    title: z.string().optional(),
-    description: z.string().optional(),
-    enum: z.array(z.string()),
-    enumNames: z.array(z.string()).optional(),
-    default: z.string().optional()
-});
+export const LegacyTitledEnumSchemaSchema = z
+    .object({
+        type: z.literal('string'),
+        title: z.string().optional(),
+        description: z.string().optional(),
+        enum: z.array(z.string()),
+        enumNames: z.array(z.string()).optional(),
+        default: z.string().optional()
+    })
+    .passthrough();
 
 // Combined single selection enumeration
 export const SingleSelectEnumSchemaSchema = z.union([UntitledSingleSelectEnumSchemaSchema, TitledSingleSelectEnumSchemaSchema]);
@@ -1795,38 +1807,46 @@ export const SingleSelectEnumSchemaSchema = z.union([UntitledSingleSelectEnumSch
 /**
  * Schema for multiple-selection enumeration without display titles for options.
  */
-export const UntitledMultiSelectEnumSchemaSchema = z.object({
-    type: z.literal('array'),
-    title: z.string().optional(),
-    description: z.string().optional(),
-    minItems: z.number().optional(),
-    maxItems: z.number().optional(),
-    items: z.object({
-        type: z.literal('string'),
-        enum: z.array(z.string())
-    }),
-    default: z.array(z.string()).optional()
-});
+export const UntitledMultiSelectEnumSchemaSchema = z
+    .object({
+        type: z.literal('array'),
+        title: z.string().optional(),
+        description: z.string().optional(),
+        minItems: z.number().optional(),
+        maxItems: z.number().optional(),
+        items: z
+            .object({
+                type: z.literal('string'),
+                enum: z.array(z.string())
+            })
+            .passthrough(),
+        default: z.array(z.string()).optional()
+    })
+    .passthrough();
 
 /**
  * Schema for multiple-selection enumeration with display titles for each option.
  */
-export const TitledMultiSelectEnumSchemaSchema = z.object({
-    type: z.literal('array'),
-    title: z.string().optional(),
-    description: z.string().optional(),
-    minItems: z.number().optional(),
-    maxItems: z.number().optional(),
-    items: z.object({
-        anyOf: z.array(
-            z.object({
-                const: z.string(),
-                title: z.string()
+export const TitledMultiSelectEnumSchemaSchema = z
+    .object({
+        type: z.literal('array'),
+        title: z.string().optional(),
+        description: z.string().optional(),
+        minItems: z.number().optional(),
+        maxItems: z.number().optional(),
+        items: z
+            .object({
+                anyOf: z.array(
+                    z.object({
+                        const: z.string(),
+                        title: z.string()
+                    })
+                )
             })
-        )
-    }),
-    default: z.array(z.string()).optional()
-});
+            .passthrough(),
+        default: z.array(z.string()).optional()
+    })
+    .passthrough();
 
 /**
  * Combined schema for multiple-selection enumeration
diff --git a/packages/core/src/types/spec.types.ts b/packages/core/src/types/spec.types.ts
index ba849c546..3d499a70a 100644
--- a/packages/core/src/types/spec.types.ts
+++ b/packages/core/src/types/spec.types.ts
@@ -2879,6 +2879,7 @@ export interface StringSchema {
     maxLength?: number;
     format?: 'email' | 'uri' | 'date' | 'date-time';
     default?: string;
+    [key: string]: unknown;
 }
 
 /**
@@ -2894,6 +2895,7 @@ export interface NumberSchema {
     minimum?: number;
     maximum?: number;
     default?: number;
+    [key: string]: unknown;
 }
 
 /**
@@ -2907,6 +2909,7 @@ export interface BooleanSchema {
     title?: string;
     description?: string;
     default?: boolean;
+    [key: string]: unknown;
 }
 
 /**
@@ -2935,6 +2938,7 @@ export interface UntitledSingleSelectEnumSchema {
      * Optional default value.
      */
     default?: string;
+    [key: string]: unknown;
 }
 
 /**
@@ -2972,6 +2976,7 @@ export interface TitledSingleSelectEnumSchema {
      * Optional default value.
      */
     default?: string;
+    [key: string]: unknown;
 }
 
 /**
@@ -3020,6 +3025,7 @@ export interface UntitledMultiSelectEnumSchema {
      * Optional default value.
      */
     default?: string[];
+    [key: string]: unknown;
 }
 
 /**
@@ -3070,6 +3076,7 @@ export interface TitledMultiSelectEnumSchema {
      * Optional default value.
      */
     default?: string[];
+    [key: string]: unknown;
 }
 
 /**
@@ -3095,6 +3102,7 @@ export interface LegacyTitledEnumSchema {
      */
     enumNames?: string[];
     default?: string;
+    [key: string]: unknown;
 }
 
 /**
diff --git a/test/integration/test/server/elicitation.test.ts b/test/integration/test/server/elicitation.test.ts
index 55c989da0..47deb1678 100644
--- a/test/integration/test/server/elicitation.test.ts
+++ b/test/integration/test/server/elicitation.test.ts
@@ -161,7 +161,6 @@ function testElicitationFlow(validatorProvider: typeof ajvProvider | typeof cfWo
                     age: { type: 'integer', minimum: 0, maximum: 150 },
                     street: { type: 'string' },
                     city: { type: 'string' },
-                    // @ts-expect-error - pattern is not a valid property by MCP spec, however it is making use of the Ajv validator
                     zipCode: { type: 'string', pattern: '^[0-9]{5}$' },
                     newsletter: { type: 'boolean' },
                     notifications: { type: 'boolean' }
@@ -280,7 +279,6 @@ function testElicitationFlow(validatorProvider: typeof ajvProvider | typeof cfWo
             requestedSchema: {
                 type: 'object',
                 properties: {
-                    // @ts-expect-error - pattern is not a valid property by MCP spec, however it is making use of the Ajv validator
                     zipCode: { type: 'string', pattern: '^[0-9]{5}$' }
                 },
                 required: ['zipCode']