diff --git a/packages/mcp-common/src/json-schema-sanitize.spec.ts b/packages/mcp-common/src/json-schema-sanitize.spec.ts
new file mode 100644
index 00000000..ad0b7dca
--- /dev/null
+++ b/packages/mcp-common/src/json-schema-sanitize.spec.ts
@@ -0,0 +1,29 @@
+import { describe, expect, it } from 'vitest'
+
+import { stripNotEmptyJsonSchema } from './json-schema-sanitize'
+
+describe('stripNotEmptyJsonSchema', () => {
+	it('removes not:{} optional arms from anyOf', () => {
+		const input = {
+			properties: {
+				hint: {
+					anyOf: [{ not: {} }, { type: 'string', enum: ['wnam', 'enam'] }],
+				},
+			},
+		}
+		expect(stripNotEmptyJsonSchema(input)).toEqual({
+			properties: {
+				hint: { type: 'string', enum: ['wnam', 'enam'] },
+			},
+		})
+	})
+
+	it('leaves schemas without not:{} unchanged', () => {
+		const input = {
+			properties: {
+				page: { type: 'number' },
+			},
+		}
+		expect(stripNotEmptyJsonSchema(input)).toEqual(input)
+	})
+})
diff --git a/packages/mcp-common/src/json-schema-sanitize.ts b/packages/mcp-common/src/json-schema-sanitize.ts
new file mode 100644
index 00000000..060a9813
--- /dev/null
+++ b/packages/mcp-common/src/json-schema-sanitize.ts
@@ -0,0 +1,42 @@
+/**
+ * Remove zod-to-json-schema optional arms like `{ "not": {} }` that break strict
+ * LLM function-calling validators (Kimi, Gemini, OpenAI strict mode).
+ */
+export function stripNotEmptyJsonSchema<T>(node: T): T {
+	if (Array.isArray(node)) {
+		return node.map((item) => stripNotEmptyJsonSchema(item)) as T
+	}
+	if (node === null || typeof node !== 'object') {
+		return node
+	}
+
+	const obj = { ...(node as Record<string, unknown>) }
+
+	if (Array.isArray(obj.anyOf)) {
+		const kept = obj.anyOf.filter((member) => !isNotEmptySchema(member))
+		if (kept.length === 1) {
+			const inlined = stripNotEmptyJsonSchema(kept[0]) as Record<string, unknown>
+			const { anyOf: _removed, ...rest } = obj
+			return { ...inlined, ...rest } as T
+		}
+		obj.anyOf = kept.map((member) => stripNotEmptyJsonSchema(member))
+	}
+
+	for (const key of Object.keys(obj)) {
+		if (key === 'anyOf') continue
+		obj[key] = stripNotEmptyJsonSchema(obj[key])
+	}
+
+	return obj as T
+}
+
+function isNotEmptySchema(member: unknown): boolean {
+	if (!member || typeof member !== 'object') return false
+	const notValue = (member as Record<string, unknown>).not
+	return (
+		Object.keys(member as object).length === 1 &&
+		notValue !== null &&
+		typeof notValue === 'object' &&
+		Object.keys(notValue as object).length === 0
+	)
+}
diff --git a/packages/mcp-common/src/server.ts b/packages/mcp-common/src/server.ts
index 0cdf0269..9239f612 100644
--- a/packages/mcp-common/src/server.ts
+++ b/packages/mcp-common/src/server.ts
@@ -4,9 +4,22 @@ import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js'
 import { type ZodRawShape } from 'zod'
 
 import { MetricsTracker, SessionStart, ToolCall } from '../../mcp-observability/src'
+import * as zodJsonSchemaCompat from '@modelcontextprotocol/sdk/server/zod-json-schema-compat.js'
+
 import { buildAccountTool } from './account-tool'
+import { stripNotEmptyJsonSchema } from './json-schema-sanitize'
 import { McpError } from './mcp-error'
 
+const patchJsonSchemaCompat = zodJsonSchemaCompat as typeof zodJsonSchemaCompat & {
+	__cfSanitizePatched?: boolean
+}
+if (!patchJsonSchemaCompat.__cfSanitizePatched) {
+	const originalToJsonSchema = patchJsonSchemaCompat.toJsonSchemaCompat
+	patchJsonSchemaCompat.toJsonSchemaCompat = (schema, opts) =>
+		stripNotEmptyJsonSchema(originalToJsonSchema(schema, opts))
+	patchJsonSchemaCompat.__cfSanitizePatched = true
+}
+
 import type { ToolCallback } from '@modelcontextprotocol/sdk/server/mcp.js'
 import type { RequestHandlerExtra } from '@modelcontextprotocol/sdk/shared/protocol.js'
 import type {
diff --git a/packages/mcp-common/src/tools/d1.tools.ts b/packages/mcp-common/src/tools/d1.tools.ts
index e4463a9a..b3d91bf3 100644
--- a/packages/mcp-common/src/tools/d1.tools.ts
+++ b/packages/mcp-common/src/tools/d1.tools.ts
@@ -16,7 +16,7 @@ export function registerD1Tools(agent: CloudflareMcpAgent) {
 		'd1_databases_list',
 		'List all of the D1 databases in your Cloudflare account',
 		{
-			name: D1DatabaseNameParam.nullable().optional(),
+			name: D1DatabaseNameParam.optional(),
 			page: PaginationPageParam,
 			per_page: PaginationPerPageParam,
 		},
@@ -65,7 +65,7 @@ export function registerD1Tools(agent: CloudflareMcpAgent) {
 		'Create a new D1 database in your Cloudflare account',
 		{
 			name: D1DatabaseNameParam,
-			primary_location_hint: D1DatabasePrimaryLocationHintParam.nullable().optional(),
+			primary_location_hint: D1DatabasePrimaryLocationHintParam,
 		},
 		{
 			title: 'Create D1 database',
diff --git a/packages/mcp-common/src/tools/hyperdrive.tools.ts b/packages/mcp-common/src/tools/hyperdrive.tools.ts
index 70da37a5..d8ffd473 100644
--- a/packages/mcp-common/src/tools/hyperdrive.tools.ts
+++ b/packages/mcp-common/src/tools/hyperdrive.tools.ts
@@ -177,16 +177,15 @@ export function registerHyperdriveTools(agent: CloudflareMcpAgent) {
 		'Edit (patch) a Hyperdrive configuration in your Cloudflare account',
 		{
 			hyperdrive_id: HyperdriveConfigIdSchema,
-			name: HyperdriveConfigNameSchema.optional().nullable(),
-			database: HyperdriveOriginDatabaseSchema.optional().nullable(),
-			host: HyperdriveOriginHostSchema.optional().nullable(),
-			port: HyperdriveOriginPortSchema.optional().nullable(),
-			scheme: HyperdriveOriginSchemeSchema.optional().nullable(),
-			user: HyperdriveOriginUserSchema.optional().nullable(),
-			caching_disabled: HyperdriveCachingDisabledSchema.optional().nullable(),
-			caching_max_age: HyperdriveCachingMaxAgeSchema.optional().nullable(),
-			caching_stale_while_revalidate:
-				HyperdriveCachingStaleWhileRevalidateSchema.optional().nullable(),
+			name: HyperdriveConfigNameSchema.optional(),
+			database: HyperdriveOriginDatabaseSchema.optional(),
+			host: HyperdriveOriginHostSchema.optional(),
+			port: HyperdriveOriginPortSchema.optional(),
+			scheme: HyperdriveOriginSchemeSchema.optional(),
+			user: HyperdriveOriginUserSchema.optional(),
+			caching_disabled: HyperdriveCachingDisabledSchema.optional(),
+			caching_max_age: HyperdriveCachingMaxAgeSchema.optional(),
+			caching_stale_while_revalidate: HyperdriveCachingStaleWhileRevalidateSchema.optional(),
 		},
 		{
 			title: 'Edit Hyperdrive config',
diff --git a/packages/mcp-common/src/types/shared.types.ts b/packages/mcp-common/src/types/shared.types.ts
index fdf88dbc..9621f8d1 100644
--- a/packages/mcp-common/src/types/shared.types.ts
+++ b/packages/mcp-common/src/types/shared.types.ts
@@ -1,7 +1,7 @@
 import { z } from 'zod'
 
-export const PaginationPerPageParam = z.number().nullable().optional()
-export const PaginationPageParam = z.number().nullable().optional()
+export const PaginationPerPageParam = z.number().optional()
+export const PaginationPageParam = z.number().optional()
 
 export const PaginationLimitParam = z.number().optional()
 export const PaginationOffsetParam = z.number().optional()