diff --git a/api/server/services/ToolService.js b/api/server/services/ToolService.js
index 082217e783..8a51d0ac7f 100644
--- a/api/server/services/ToolService.js
+++ b/api/server/services/ToolService.js
@@ -1197,6 +1197,7 @@ async function loadAgentTools({
       loadedTools,
       userId: req.user.id,
       agentId: agent.id,
+      provider: agent.provider,
       agentToolOptions: agent.tool_options,
       deferredToolsEnabled,
       programmaticToolsEnabled,
diff --git a/packages/api/src/mcp/__tests__/zod.spec.ts b/packages/api/src/mcp/__tests__/zod.spec.ts
index 03ff634097..85a183acec 100644
--- a/packages/api/src/mcp/__tests__/zod.spec.ts
+++ b/packages/api/src/mcp/__tests__/zod.spec.ts
@@ -2907,4 +2907,112 @@ describe('sanitizeGeminiSchema', () => {
       },
     });
   });
+
+  it('strips unresolvable `$ref` keys that survive ref resolution (Gemini rejects them)', () => {
+    const schema = {
+      type: 'object',
+      properties: {
+        recurrence: { $ref: 'https://example.com/external.json', description: 'Recurrence rule' },
+      },
+    } as any;
+    expect(sanitizeGeminiSchema(schema)).toEqual({
+      type: 'object',
+      properties: {
+        recurrence: { description: 'Recurrence rule' },
+      },
+    });
+  });
+});
+
+describe('resolveJsonSchemaRefs local pointer refs', () => {
+  it('resolves a `#/properties/...` pointer against the root schema', () => {
+    const schema = {
+      type: 'object' as const,
+      properties: {
+        body: {
+          type: 'object' as const,
+          properties: {
+            start: {
+              type: 'object' as const,
+              properties: {
+                dateTime: { type: 'string' as const },
+                timeZone: { type: 'string' as const },
+              },
+            },
+            end: { $ref: '#/properties/body/properties/start' },
+          },
+        },
+      },
+    };
+
+    const resolved = resolveJsonSchemaRefs(schema);
+    expect(resolved.properties?.body?.properties?.end).toEqual({
+      type: 'object',
+      properties: {
+        dateTime: { type: 'string' },
+        timeZone: { type: 'string' },
+      },
+    });
+    expect(JSON.stringify(resolved)).not.toContain('$ref');
+  });
+
+  it('resolves pointers that traverse array indices (e.g. anyOf members)', () => {
+    const schema = {
+      type: 'object' as const,
+      properties: {
+        daysOfWeek: {
+          type: 'array' as const,
+          items: {
+            anyOf: [{ type: 'string' as const, enum: ['monday', 'tuesday'] }],
+          },
+        },
+        firstDayOfWeek: { $ref: '#/properties/daysOfWeek/items/anyOf/0' },
+      },
+    };
+
+    const resolved = resolveJsonSchemaRefs(schema);
+    expect(resolved.properties?.firstDayOfWeek).toEqual({
+      type: 'string',
+      enum: ['monday', 'tuesday'],
+    });
+  });
+
+  it('breaks mutually circular local pointers without hanging', () => {
+    const schema = {
+      type: 'object' as const,
+      properties: {
+        a: { $ref: '#/properties/b' },
+        b: { $ref: '#/properties/a' },
+      },
+    };
+
+    const resolved = resolveJsonSchemaRefs(schema);
+    expect(resolved.properties?.a).toEqual({ type: 'object' });
+    expect(resolved.properties?.b).toEqual({ type: 'object' });
+  });
+
+  it('keeps dangling local pointers as-is', () => {
+    const schema = {
+      type: 'object' as const,
+      properties: {
+        broken: { $ref: '#/properties/missing/nested' },
+      },
+    };
+
+    const resolved = resolveJsonSchemaRefs(schema);
+    expect(resolved.properties?.broken).toEqual({ $ref: '#/properties/missing/nested' });
+  });
+
+  it('unescapes RFC 6901 tokens (~0 → ~, ~1 → /) in pointer segments', () => {
+    const schema = {
+      type: 'object' as const,
+      properties: {
+        'a/b': { type: 'string' as const },
+        alias: { $ref: '#/properties/a~1b' },
+      },
+    };
+
+    const resolved = resolveJsonSchemaRefs(schema);
+    expect(resolved.properties?.alias).toEqual({ type: 'string' });
+  });
 });
diff --git a/packages/api/src/mcp/zod.ts b/packages/api/src/mcp/zod.ts
index 767c1919a5..ac87eabd87 100644
--- a/packages/api/src/mcp/zod.ts
+++ b/packages/api/src/mcp/zod.ts
@@ -173,22 +173,57 @@ function convertToZodUnion(
 }
 
 /**
- * Helper function to resolve $ref references
+ * Resolves a local JSON pointer (e.g. `#/properties/body/properties/start`)
+ * against the root schema, per RFC 6901 (`~1` → `/`, `~0` → `~`).
+ * @returns The referenced subschema, or undefined when the pointer is dangling
+ */
+function resolveLocalPointer(
+  root: Record<string, unknown>,
+  pointer: string,
+): Record<string, unknown> | undefined {
+  const segments = pointer
+    .slice(2)
+    .split('/')
+    .map((segment) => segment.replace(/~1/g, '/').replace(/~0/g, '~'));
+
+  let node: unknown = root;
+  for (const segment of segments) {
+    if (node == null || typeof node !== 'object') {
+      return undefined;
+    }
+    node = (node as Record<string, unknown>)[segment];
+  }
+
+  if (node != null && typeof node === 'object' && !Array.isArray(node)) {
+    return node as Record<string, unknown>;
+  }
+  return undefined;
+}
+
+/**
+ * Helper function to resolve $ref references. Resolves `#/$defs/...` and
+ * `#/definitions/...` refs via the definitions map, and any other local
+ * `#/...` pointer (e.g. `#/properties/foo`) against the root schema —
+ * MCP servers with OpenAPI-derived schemas commonly emit both forms.
  * @param schema - The schema to resolve
  * @param definitions - The definitions to use
  * @param visited - The set of visited references
+ * @param root - The root schema local pointers resolve against (defaults to `schema`)
  * @returns The resolved schema
  */
 export function resolveJsonSchemaRefs<T extends Record<string, unknown>>(
   schema: T,
   definitions?: Record<string, unknown>,
   visited: Set<string> = new Set<string>(),
+  root?: Record<string, unknown>,
 ): T {
   // Handle null, undefined, or non-object values first
   if (!schema || typeof schema !== 'object') {
     return schema;
   }
 
+  const rootSchema = root ?? schema;
+
   // If no definitions provided, try to extract from schema.$defs or schema.definitions
   if (!definitions) {
     definitions = (schema.$defs || schema.definitions) as Record<string, unknown>;
@@ -196,7 +231,9 @@ export function resolveJsonSchemaRefs<T extends Record<string, unknown>>(
 
   // Handle arrays
   if (Array.isArray(schema)) {
-    return schema.map((item) => resolveJsonSchemaRefs(item, definitions, visited)) as unknown as T;
+    return schema.map((item) =>
+      resolveJsonSchemaRefs(item, definitions, visited, rootSchema),
+    ) as unknown as T;
   }
 
   // Handle objects
@@ -219,7 +256,12 @@ export function resolveJsonSchemaRefs<T extends Record<string, unknown>>(
 
       // Extract the reference path
       const refPath = value.replace(/^#\/(\$defs|definitions)\//, '');
-      const resolved = definitions?.[refPath];
+      let resolved = definitions?.[refPath];
+
+      // Fall back to resolving any other local pointer against the root schema
+      if (!resolved && value.startsWith('#/')) {
+        resolved = resolveLocalPointer(rootSchema, value);
+      }
 
       if (resolved) {
         visited.add(value);
@@ -227,6 +269,7 @@ export function resolveJsonSchemaRefs<T extends Record<string, unknown>>(
           resolved as Record<string, unknown>,
           definitions,
           visited,
+          rootSchema,
         );
         visited.delete(value);
 
@@ -238,7 +281,12 @@ export function resolveJsonSchemaRefs<T extends Record<string, unknown>>(
       }
     } else if (value && typeof value === 'object') {
       // Recursively resolve nested objects/arrays
-      result[key] = resolveJsonSchemaRefs(value as Record<string, unknown>, definitions, visited);
+      result[key] = resolveJsonSchemaRefs(
+        value as Record<string, unknown>,
+        definitions,
+        visited,
+        rootSchema,
+      );
     } else {
       // Copy primitive values as is
       result[key] = value;
@@ -367,6 +415,7 @@ function mergeRequired(a: unknown, b: unknown): string[] | undefined {
 const GEMINI_UNSUPPORTED_KEYS = new Set([
   'additionalProperties',
   '$schema',
+  '$ref',
   '$id',
   'id',
   '$comment',
diff --git a/packages/api/src/tools/classification.spec.ts b/packages/api/src/tools/classification.spec.ts
index 66cdfd4611..b543d2bad1 100644
--- a/packages/api/src/tools/classification.spec.ts
+++ b/packages/api/src/tools/classification.spec.ts
@@ -1,3 +1,4 @@
+import { Providers } from '@librechat/agents';
 import type { AgentToolOptions } from 'librechat-data-provider';
 import type { GenericTool } from '@librechat/agents';
 import type { LCToolRegistry } from './classification';
@@ -338,6 +339,77 @@ describe('classification.ts', () => {
       expect(result.toolRegistry?.has('tool_search')).toBe(true);
     });
 
+    type ToolSearchParams = {
+      properties?: Record<string, { oneOf?: unknown[]; type?: string }>;
+    };
+
+    it('should sanitize the tool_search schema for Google providers (no union types)', async () => {
+      const loadedTools: GenericTool[] = [createMCPTool('tool1')];
+
+      const agentToolOptions: AgentToolOptions = {
+        tool1: { defer_loading: true },
+      };
+
+      const result = await buildToolClassification({
+        loadedTools,
+        userId: 'user1',
+        agentId: 'agent1',
+        agentToolOptions,
+        deferredToolsEnabled: true,
+        definitionsOnly: true,
+        provider: Providers.GOOGLE,
+      });
+
+      const toolSearchDef = result.toolDefinitions.find((d) => d.name === 'tool_search');
+      const params = toolSearchDef?.parameters as ToolSearchParams | undefined;
+      expect(params?.properties?.mcp_server?.oneOf).toBeUndefined();
+      expect(params?.properties?.mcp_server?.type).toBe('string');
+    });
+
+    it('should sanitize the tool_search instance schema for Vertex AI provider', async () => {
+      const loadedTools: GenericTool[] = [createMCPTool('tool1')];
+
+      const agentToolOptions: AgentToolOptions = {
+        tool1: { defer_loading: true },
+      };
+
+      const result = await buildToolClassification({
+        loadedTools,
+        userId: 'user1',
+        agentId: 'agent1',
+        agentToolOptions,
+        deferredToolsEnabled: true,
+        provider: Providers.VERTEXAI,
+      });
+
+      const toolSearchTool = result.additionalTools.find((t) => t.name === 'tool_search');
+      const schema = (toolSearchTool as unknown as { schema: ToolSearchParams }).schema;
+      expect(schema.properties?.mcp_server?.oneOf).toBeUndefined();
+      expect(schema.properties?.mcp_server?.type).toBe('string');
+    });
+
+    it('should keep the original tool_search schema for non-Google providers', async () => {
+      const loadedTools: GenericTool[] = [createMCPTool('tool1')];
+
+      const agentToolOptions: AgentToolOptions = {
+        tool1: { defer_loading: true },
+      };
+
+      const result = await buildToolClassification({
+        loadedTools,
+        userId: 'user1',
+        agentId: 'agent1',
+        agentToolOptions,
+        deferredToolsEnabled: true,
+        definitionsOnly: true,
+        provider: Providers.OPENAI,
+      });
+
+      const toolSearchDef = result.toolDefinitions.find((d) => d.name === 'tool_search');
+      const params = toolSearchDef?.parameters as ToolSearchParams | undefined;
+      expect(Array.isArray(params?.properties?.mcp_server?.oneOf)).toBe(true);
+    });
+
     it('should add PTC definition when definitionsOnly=true and capabilities allow programmatic tools', async () => {
       const loadedTools: GenericTool[] = [createMCPTool('tool1')];
 
diff --git a/packages/api/src/tools/classification.ts b/packages/api/src/tools/classification.ts
index eaf4ff0953..b461c85990 100644
--- a/packages/api/src/tools/classification.ts
+++ b/packages/api/src/tools/classification.ts
@@ -8,12 +8,12 @@
 import { logger } from '@librechat/data-schemas';
 import { Constants } from 'librechat-data-provider';
 import {
+  Providers,
   createToolSearch,
   ToolSearchToolDefinition,
   BashProgrammaticToolCallingDefinition,
   createBashProgrammaticToolCallingTool,
 } from '@librechat/agents';
-import type { AgentToolOptions } from 'librechat-data-provider';
 import type {
   LCToolRegistry,
   JsonSchemaType,
@@ -21,6 +21,8 @@ import type {
   GenericTool,
   LCTool,
 } from '@librechat/agents';
+import type { AgentToolOptions } from 'librechat-data-provider';
+import { sanitizeGeminiSchema } from '~/mcp/zod';
 
 export type { LCTool, LCToolRegistry, AllowedCaller, JsonSchemaType };
 
@@ -191,6 +193,8 @@ export interface BuildToolClassificationParams {
   codeExecutionEnabled?: boolean;
   /** When true, skip creating tool instances (for event-driven mode) */
   definitionsOnly?: boolean;
+  /** Agent provider — Gemini/Vertex rejects union types, so injected tool schemas get sanitized */
+  provider?: Providers | string;
   /** Optional host-supplied Code API auth headers for remote programmatic execution. */
   authHeaders?: () => Promise<Record<string, string>> | Record<string, string>;
 }
@@ -253,6 +257,7 @@ export async function buildToolClassification(
 ): Promise<BuildToolClassificationResult> {
   const {
     agentId,
+    provider,
     loadedTools,
     agentToolOptions,
     definitionsOnly = false,
@@ -261,6 +266,7 @@ export async function buildToolClassification(
     codeExecutionEnabled = false,
     authHeaders,
   } = params;
+  const isGoogle = provider === Providers.GOOGLE || provider === Providers.VERTEXAI;
   const additionalTools: GenericTool[] = [];
 
   const mcpTools = loadedTools.filter(isMCPTool);
@@ -311,11 +317,22 @@ export async function buildToolClassification(
 
   /** Tool search uses local mode (no API key needed) */
   if (hasDeferredTools) {
+    /**
+     * The ToolSearch schema declares `mcp_server` as a string/array union, which
+     * `zod_to_gemini_parameters` rejects — collapse it for Gemini/Vertex agents.
+     */
+    const toolSearchParameters = (isGoogle
+      ? sanitizeGeminiSchema(ToolSearchToolDefinition.schema as Record<string, unknown>)
+      : ToolSearchToolDefinition.schema) as unknown as LCTool['parameters'];
+
     if (!definitionsOnly) {
       const toolSearchTool = createToolSearch({
         mode: 'local',
         toolRegistry,
       });
+      if (isGoogle) {
+        toolSearchTool.schema = toolSearchParameters as typeof toolSearchTool.schema;
+      }
       additionalTools.push(toolSearchTool);
     }
 
@@ -323,7 +340,7 @@ export async function buildToolClassification(
     toolDefinitions.push({
       name: ToolSearchToolDefinition.name,
       description: ToolSearchToolDefinition.description,
-      parameters: ToolSearchToolDefinition.schema as unknown as LCTool['parameters'],
+      parameters: toolSearchParameters,
     });
     toolRegistry.set(ToolSearchToolDefinition.name, {
       name: ToolSearchToolDefinition.name,
diff --git a/packages/api/src/tools/definitions.ts b/packages/api/src/tools/definitions.ts
index 4babe3ed81..16d689807b 100644
--- a/packages/api/src/tools/definitions.ts
+++ b/packages/api/src/tools/definitions.ts
@@ -212,6 +212,7 @@ export async function loadToolDefinitions(
   const classificationResult = await buildToolClassification({
     userId,
     agentId,
+    provider,
     loadedTools,
     deferredToolsEnabled,
     programmaticToolsEnabled,