@ai-sdk/mcp - npm Package Compare versions

Comparing version 2.0.32 to 2.0.33

src/tool/mcp-http-headers.ts

+import { convertUint8ArrayToBase64, isRecord } from '@ai-sdk/provider-utils';
+
+type HeaderValueType = 'boolean' | 'integer' | 'string';
+
+export type MCPToolHeaderBinding = {
+  headerName: string;
+  path: string[];
+  valueType: HeaderValueType;
+};
+
+export type MCPToolHeaderBindingsResult =
+  | { success: true; bindings: MCPToolHeaderBinding[] }
+  | { success: false; error: string };
+
+const HTTP_TOKEN_PATTERN = /^[!#$%&'*+\-.^_`|~0-9A-Za-z]+$/;
+const BASE64_SENTINEL_PATTERN = /^=\?base64\?.*\?=$/;
+
+export function encodeMCPHeaderValue(value: string): string {
+  const isPlainAscii = [...value].every(character => {
+    const code = character.charCodeAt(0);
+    return code === 0x09 || (code >= 0x20 && code <= 0x7e);
+  });
+
+  if (
+    isPlainAscii &&
+    value.trim() === value &&
+    !BASE64_SENTINEL_PATTERN.test(value)
+  ) {
+    return value;
+  }
+
+  return `=?base64?${convertUint8ArrayToBase64(new TextEncoder().encode(value))}?=`;
+}
+
+export function getMCPToolHeaderBindings(
+  inputSchema: unknown,
+): MCPToolHeaderBindingsResult {
+  if (!isRecord(inputSchema)) {
+    return {
+      success: false,
+      error: 'inputSchema must be a JSON Schema object',
+    };
+  }
+
+  const bindings: MCPToolHeaderBinding[] = [];
+  const headerNames = new Set<string>();
+  let error: string | undefined;
+
+  const visit = (
+    value: unknown,
+    path: string[],
+    staticallyReachable: boolean,
+  ): void => {
+    if (error != null || !isRecord(value)) {
+      return;
+    }
+
+    if ('x-mcp-header' in value) {
+      if (!staticallyReachable || path.length === 0) {
+        error = 'x-mcp-header is not on a statically reachable property';
+        return;
+      }
+
+      const headerName = value['x-mcp-header'];
+      if (
+        typeof headerName !== 'string' ||
+        !HTTP_TOKEN_PATTERN.test(headerName)
+      ) {
+        error = 'x-mcp-header must be a non-empty HTTP token';
+        return;
+      }
+
+      const normalizedHeaderName = headerName.toLowerCase();
+      if (headerNames.has(normalizedHeaderName)) {
+        error = `x-mcp-header value "${headerName}" is not unique`;
+        return;
+      }
+
+      const valueType = value.type;
+      if (
+        valueType !== 'boolean' &&
+        valueType !== 'integer' &&
+        valueType !== 'string'
+      ) {
+        error =
+          'x-mcp-header can only annotate boolean, integer, or string properties';
+        return;
+      }
+
+      headerNames.add(normalizedHeaderName);
+      bindings.push({ headerName, path, valueType });
+    }
+
+    for (const [key, child] of Object.entries(value)) {
+      if (key === 'x-mcp-header') {
+        continue;
+      }
+
+      if (key === 'properties' && isRecord(child)) {
+        for (const [propertyName, propertySchema] of Object.entries(child)) {
+          visit(propertySchema, [...path, propertyName], staticallyReachable);
+        }
+      } else {
+        visit(child, path, false);
+      }
+    }
+  };
+
+  visit(inputSchema, [], true);
+
+  return error == null
+    ? { success: true, bindings }
+    : { success: false, error };
+}
+
+function getValueAtPath(
+  value: Record<string, unknown>,
+  path: string[],
+): unknown {
+  let current: unknown = value;
+  for (const segment of path) {
+    if (!isRecord(current)) {
+      return undefined;
+    }
+    current = current[segment];
+  }
+  return current;
+}
+
+export function createMCPToolHeaders({
+  bindings,
+  args,
+}: {
+  bindings: MCPToolHeaderBinding[];
+  args: Record<string, unknown>;
+}): Record<string, string> {
+  const headers: Record<string, string> = {};
+
+  for (const binding of bindings) {
+    const value = getValueAtPath(args, binding.path);
+    if (value == null) {
+      continue;
+    }
+
+    if (
+      (binding.valueType === 'string' && typeof value !== 'string') ||
+      (binding.valueType === 'boolean' && typeof value !== 'boolean') ||
+      (binding.valueType === 'integer' && !Number.isSafeInteger(value))
+    ) {
+      throw new TypeError(
+        `Tool argument "${binding.path.join('.')}" does not match its x-mcp-header type`,
+      );
+    }
+
+    headers[`Mcp-Param-${binding.headerName}`] = encodeMCPHeaderValue(
+      String(value),
+    );
+  }
+
+  return headers;
+}

CHANGELOG.md

 # @ai-sdk/mcp
 
+## 2.0.33
+
+### Patch Changes
+
+- 1f29230: feat(mcp): harden oauth client registration according to latest protocol
+- 0c60a40: feat(mcp): add mcp 2026 streamable HTTP support
+- e6a9927: feat(mcp): add the latest 2026 protocol discovery foundation
+
 ## 2.0.32
@@ -4,0 +12,0 @@

dist/index.d.ts

@@ -19,2 +19,3 @@ import { z } from 'zod/v4';
         _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+        resultType: z.ZodOptional<z.ZodString>;
     }, z.core.$loose>;
@@ -25,3 +26,3 @@ }, z.core.$strict>;
     jsonrpc: z.ZodLiteral<"2.0">;
-    id: z.ZodUnion<readonly [z.ZodString, z.ZodNumber]>;
+    id: z.ZodOptional<z.ZodUnion<readonly [z.ZodString, z.ZodNumber]>>;
     error: z.ZodObject<{
@@ -60,6 +61,7 @@ code: z.ZodNumber;
         _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+        resultType: z.ZodOptional<z.ZodString>;
     }, z.core.$loose>;
 }, z.core.$strict>, z.ZodObject<{
     jsonrpc: z.ZodLiteral<"2.0">;
-    id: z.ZodUnion<readonly [z.ZodString, z.ZodNumber]>;
+    id: z.ZodOptional<z.ZodUnion<readonly [z.ZodString, z.ZodNumber]>>;
     error: z.ZodObject<{
@@ -84,2 +86,3 @@ code: z.ZodNumber;
     refresh_token: z.ZodOptional<z.ZodString>;
+    issuer: z.ZodOptional<z.ZodString>;
     authorization_server: z.ZodOptional<z.ZodString>;
@@ -93,2 +96,4 @@ token_endpoint: z.ZodOptional<z.ZodString>;
     registration_endpoint: z.ZodOptional<z.ZodString>;
+    authorization_response_iss_parameter_supported: z.ZodOptional<z.ZodBoolean>;
+    client_id_metadata_document_supported: z.ZodOptional<z.ZodBoolean>;
     scopes_supported: z.ZodOptional<z.ZodArray<z.ZodString>>;
@@ -113,2 +118,4 @@ response_types_supported: z.ZodArray<z.ZodString>;
     registration_endpoint: z.ZodOptional<z.ZodString>;
+    authorization_response_iss_parameter_supported: z.ZodOptional<z.ZodBoolean>;
+    client_id_metadata_document_supported: z.ZodOptional<z.ZodBoolean>;
     scopes_supported: z.ZodOptional<z.ZodArray<z.ZodString>>;
@@ -128,2 +135,3 @@ response_types_supported: z.ZodArray<z.ZodString>;
     client_secret_expires_at: z.ZodOptional<z.ZodNumber>;
+    issuer: z.ZodOptional<z.ZodString>;
     authorization_server: z.ZodOptional<z.ZodString>;
@@ -134,2 +142,3 @@ token_endpoint: z.ZodOptional<z.ZodString>;
     redirect_uris: z.ZodArray<z.ZodString>;
+    application_type: z.ZodOptional<z.ZodUnion<readonly [z.ZodLiteral<"native">, z.ZodLiteral<"web">]>>;
     token_endpoint_auth_method: z.ZodOptional<z.ZodString>;
@@ -160,2 +169,3 @@ grant_types: z.ZodOptional<z.ZodArray<z.ZodString>>;
 interface OAuthAuthorizationServerInformation {
+    issuer?: string;
     authorizationServerUrl: string;
@@ -221,2 +231,6 @@ tokenEndpoint: string;
     callbackState?: string;
+    /**
+     * Value of the `iss` parameter from the authorization response.
+     */
+    callbackIssuer?: string;
     scope?: string;
@@ -237,2 +251,6 @@ resourceMetadataUrl?: URL;
     /**
+     * Request-specific HTTP headers produced from MCP tool parameters.
+     */
+    headers?: Record<string, string>;
+    /**
      * Associates an outgoing message with an incoming request.
@@ -258,2 +276,14 @@ */
     /**
+     * Whether this transport can probe for stateless MCP protocol versions.
+     *
+     * Custom transports default to the legacy initialization flow unless they
+     * explicitly opt in.
+     */
+    supportsProtocolVersionDiscovery?: boolean;
+    /**
+     * Whether this transport mirrors x-mcp-header tool parameters into request
+     * headers.
+     */
+    supportsMcpToolParameterHeaders?: boolean;
+    /**
      * Initialize and start the transport
@@ -412,2 +442,3 @@ */
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     protocolVersion: z.ZodString;
@@ -447,2 +478,3 @@ capabilities: z.ZodObject<{
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     nextCursor: z.ZodOptional<z.ZodString>;
@@ -454,3 +486,3 @@ tools: z.ZodArray<z.ZodObject<{
         inputSchema: z.ZodObject<{
-            type: z.ZodLiteral<"object">;
+            type: z.ZodOptional<z.ZodUnknown>;
             properties: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
@@ -468,2 +500,3 @@ }, z.core.$loose>;
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     nextCursor: z.ZodOptional<z.ZodString>;
@@ -482,2 +515,3 @@ resources: z.ZodArray<z.ZodObject<{
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     content: z.ZodArray<z.ZodUnion<readonly [z.ZodObject<{
@@ -516,2 +550,3 @@ type: z.ZodLiteral<"text">;
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     toolResult: z.ZodUnknown;
@@ -522,2 +557,3 @@ }, z.core.$loose>]>;
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     resourceTemplates: z.ZodArray<z.ZodObject<{
@@ -534,2 +570,3 @@ uriTemplate: z.ZodString;
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     contents: z.ZodArray<z.ZodUnion<readonly [z.ZodObject<{
@@ -570,2 +607,3 @@ uri: z.ZodString;
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     completion: z.ZodObject<{
@@ -580,2 +618,3 @@ values: z.ZodArray<z.ZodString>;
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     nextCursor: z.ZodOptional<z.ZodString>;
@@ -596,2 +635,3 @@ prompts: z.ZodArray<z.ZodObject<{
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     description: z.ZodOptional<z.ZodString>;
@@ -643,2 +683,3 @@ messages: z.ZodArray<z.ZodObject<{
     _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+    resultType: z.ZodOptional<z.ZodString>;
     action: z.ZodUnion<readonly [z.ZodLiteral<"accept">, z.ZodLiteral<"decline">, z.ZodLiteral<"cancel">]>;
@@ -653,2 +694,12 @@ content: z.ZodOptional<z.ZodRecord<z.ZodString, z.ZodUnknown>>;
     /**
+     * Whether transports that support stateless protocol discovery should probe
+     * with `server/discover` before falling back to legacy initialization.
+     *
+     * Disable this for legacy servers that require `initialize` to be the first
+     * request.
+     *
+     * @default true
+     */
+    protocolVersionDiscovery?: boolean;
+    /**
      * Options that bound or cancel transport startup and the initialize request.
@@ -655,0 +706,0 @@ */

dist/mcp-stdio/index.d.ts

@@ -23,6 +23,7 @@ import { IOType } from 'node:child_process';
         _meta: z.ZodOptional<z.ZodObject<{}, z.core.$loose>>;
+        resultType: z.ZodOptional<z.ZodString>;
     }, z.core.$loose>;
 }, z.core.$strict>, z.ZodObject<{
     jsonrpc: z.ZodLiteral<"2.0">;
-    id: z.ZodUnion<readonly [z.ZodString, z.ZodNumber]>;
+    id: z.ZodOptional<z.ZodUnion<readonly [z.ZodString, z.ZodNumber]>>;
     error: z.ZodObject<{
@@ -46,2 +47,6 @@ code: z.ZodNumber;
     /**
+     * Request-specific HTTP headers produced from MCP tool parameters.
+     */
+    headers?: Record<string, string>;
+    /**
      * Associates an outgoing message with an incoming request.
@@ -67,2 +72,14 @@ */
     /**
+     * Whether this transport can probe for stateless MCP protocol versions.
+     *
+     * Custom transports default to the legacy initialization flow unless they
+     * explicitly opt in.
+     */
+    supportsProtocolVersionDiscovery?: boolean;
+    /**
+     * Whether this transport mirrors x-mcp-header tool parameters into request
+     * headers.
+     */
+    supportsMcpToolParameterHeaders?: boolean;
+    /**
      * Initialize and start the transport
@@ -112,2 +129,3 @@ */
 declare class StdioMCPTransport implements MCPTransport {
+    readonly supportsProtocolVersionDiscovery = true;
     private process?;
@@ -114,0 +132,0 @@ private abortController;

dist/mcp-stdio/index.js

@@ -16,3 +16,5 @@ // src/tool/json-rpc-message.ts
 });
-var ResultSchema = BaseParamsSchema;
+var ResultSchema = BaseParamsSchema.extend({
+  resultType: z.optional(z.string())
+});
 var RequestSchema = z.object({
@@ -50,2 +52,9 @@ method: z.string(),
 }).loose();
+var DiscoverResultSchema = ResultSchema.extend({
+  supportedVersions: z.array(z.string()),
+  capabilities: ServerCapabilitiesSchema,
+  instructions: z.optional(z.string()),
+  ttlMs: z.optional(z.number()),
+  cacheScope: z.optional(z.union([z.literal("public"), z.literal("private")]))
+});
 var InitializeResultSchema = ResultSchema.extend({
@@ -67,6 +76,6 @@ protocolVersion: z.string(),
   description: z.optional(z.string()),
-  inputSchema: z.object({
-    type: z.literal("object"),
+  inputSchema: z.looseObject({
+    type: z.optional(z.unknown()),
     properties: z.optional(z.object({}).loose())
-  }).loose(),
+  }),
   /**
@@ -260,3 +269,3 @@ * @see https://modelcontextprotocol.io/specification/2025-06-18/server/tools#output-schema
   jsonrpc: z2.literal(JSONRPC_VERSION),
-  id: z2.union([z2.string(), z2.number().int()]),
+  id: z2.optional(z2.union([z2.string(), z2.number().int()])),
   error: z2.object({
@@ -370,2 +379,3 @@ code: z2.number().int(),
   constructor(server) {
+    this.supportsProtocolVersionDiscovery = true;
     this.abortController = new AbortController();
@@ -372,0 +382,0 @@ this.readBuffer = new ReadBuffer();

dist/mcp-stdio/index.js.map

@@ -1,1 +0,1 @@
-{"version":3,"sources":["../../src/tool/json-rpc-message.ts","../../src/tool/types.ts","../../src/error/mcp-client-error.ts","../../src/tool/mcp-stdio/create-child-process.ts","../../src/tool/mcp-stdio/get-environment.ts","../../src/tool/mcp-stdio/mcp-stdio-transport.ts"],"sourcesContent":["import { parseJSON } from '@ai-sdk/provider-utils';\nimport { z } from 'zod/v4';\nimport { BaseParamsSchema, RequestSchema, ResultSchema } from './types';\n\nconst JSONRPC_VERSION = '2.0';\n\nconst JSONRPCRequestSchema = z\n  .object({\n    jsonrpc: z.literal(JSONRPC_VERSION),\n    id: z.union([z.string(), z.number().int()]),\n  })\n  .merge(RequestSchema)\n  .strict();\n\nexport type JSONRPCRequest = z.infer<typeof JSONRPCRequestSchema>;\n\nconst JSONRPCResponseSchema = z\n  .object({\n    jsonrpc: z.literal(JSONRPC_VERSION),\n    id: z.union([z.string(), z.number().int()]),\n    result: ResultSchema,\n  })\n  .strict();\n\nexport type JSONRPCResponse = z.infer<typeof JSONRPCResponseSchema>;\n\nconst JSONRPCErrorSchema = z\n  .object({\n    jsonrpc: z.literal(JSONRPC_VERSION),\n    id: z.union([z.string(), z.number().int()]),\n    error: z.object({\n      code: z.number().int(),\n      message: z.string(),\n      data: z.optional(z.unknown()),\n    }),\n  })\n  .strict();\n\nexport type JSONRPCError = z.infer<typeof JSONRPCErrorSchema>;\n\nconst JSONRPCNotificationSchema = z\n  .object({\n    jsonrpc: z.literal(JSONRPC_VERSION),\n  })\n  .merge(\n    z.object({\n      method: z.string(),\n      params: z.optional(BaseParamsSchema),\n    }),\n  )\n  .strict();\n\nexport type JSONRPCNotification = z.infer<typeof JSONRPCNotificationSchema>;\n\nexport const JSONRPCMessageSchema = z.union([\n  JSONRPCRequestSchema,\n  JSONRPCNotificationSchema,\n  JSONRPCResponseSchema,\n  JSONRPCErrorSchema,\n]);\n\nexport type JSONRPCMessage = z.infer<typeof JSONRPCMessageSchema>;\n\nexport function validateJSONRPCMessage(message: unknown): JSONRPCMessage {\n  return JSONRPCMessageSchema.parse(message);\n}\n\nexport async function parseJSONRPCMessage(\n  text: string,\n): Promise<JSONRPCMessage> {\n  return validateJSONRPCMessage(await parseJSON({ text }));\n}\n","import { z } from 'zod/v4';\nimport type { JSONObject } from '@ai-sdk/provider';\nimport type { FlexibleSchema, Tool } from '@ai-sdk/provider-utils';\n\nexport const LATEST_PROTOCOL_VERSION = '2025-11-25';\nexport const SUPPORTED_PROTOCOL_VERSIONS = [\n  LATEST_PROTOCOL_VERSION,\n  '2025-06-18',\n  '2025-03-26',\n  '2024-11-05',\n];\n\nexport type McpProviderMetadata = {\n  clientName?: string;\n  title?: string;\n  toolName?: string;\n  app?: JSONObject;\n};\n\n/** MCP tool metadata - keys should follow MCP _meta key format specification */\nconst ToolMetaSchema = z.optional(z.record(z.string(), z.unknown()));\nexport type ToolMeta = z.infer<typeof ToolMetaSchema>;\n\nexport type ToolSchemas =\n  | Record<\n      string,\n      {\n        inputSchema: FlexibleSchema<JSONObject | unknown>;\n        outputSchema?: FlexibleSchema<JSONObject | unknown>;\n      }\n    >\n  | 'automatic'\n  | undefined;\n\n/** Base MCP tool type with execute and _meta */\ntype McpToolBase<INPUT = unknown, OUTPUT = CallToolResult> = Tool<\n  INPUT,\n  OUTPUT\n> &\n  Required<Pick<Tool<INPUT, OUTPUT>, 'execute'>> & {\n    _meta?: ToolMeta;\n  };\n\nexport type McpToolSet<TOOL_SCHEMAS extends ToolSchemas = 'automatic'> =\n  TOOL_SCHEMAS extends Record<\n    string,\n    { inputSchema: FlexibleSchema<any>; outputSchema?: FlexibleSchema<any> }\n  >\n    ? {\n        [K in keyof TOOL_SCHEMAS]: TOOL_SCHEMAS[K] extends {\n          inputSchema: FlexibleSchema<infer INPUT>;\n          outputSchema: FlexibleSchema<infer OUTPUT>;\n        }\n          ? McpToolBase<INPUT, OUTPUT>\n          : TOOL_SCHEMAS[K] extends {\n                inputSchema: FlexibleSchema<infer INPUT>;\n              }\n            ? McpToolBase<INPUT, CallToolResult>\n            : never;\n      }\n    : Record<string, McpToolBase<unknown, CallToolResult>>;\n\nconst ClientOrServerImplementationSchema = z.looseObject({\n  name: z.string(),\n  version: z.string(),\n  title: z.optional(z.string()),\n});\n\n// Maps to `Implementation` in the MCP specification\nexport type Configuration = z.infer<typeof ClientOrServerImplementationSchema>;\n\nexport const BaseParamsSchema = z.looseObject({\n  _meta: z.optional(z.object({}).loose()),\n});\ntype BaseParams = z.infer<typeof BaseParamsSchema>;\nexport const ResultSchema = BaseParamsSchema;\n\nexport const RequestSchema = z.object({\n  method: z.string(),\n  params: z.optional(BaseParamsSchema),\n});\nexport type Request = z.infer<typeof RequestSchema>;\nexport type RequestOptions = {\n  signal?: AbortSignal;\n  timeout?: number;\n  maxTotalTimeout?: number;\n};\n\nexport type Notification = z.infer<typeof RequestSchema>;\n\n/** @see https://modelcontextprotocol.io/specification/2025-06-18/client/elicitation */\nconst ElicitationCapabilitySchema = z\n  .object({\n    applyDefaults: z.optional(z.boolean()),\n  })\n  .loose();\n\nconst ServerCapabilitiesSchema = z.looseObject({\n  experimental: z.optional(z.object({}).loose()),\n  logging: z.optional(z.object({}).loose()),\n  completions: z.optional(z.object({}).loose()),\n  prompts: z.optional(\n    z.looseObject({\n      listChanged: z.optional(z.boolean()),\n    }),\n  ),\n  resources: z.optional(\n    z.looseObject({\n      subscribe: z.optional(z.boolean()),\n      listChanged: z.optional(z.boolean()),\n    }),\n  ),\n  tools: z.optional(\n    z.looseObject({\n      listChanged: z.optional(z.boolean()),\n    }),\n  ),\n  elicitation: z.optional(ElicitationCapabilitySchema),\n});\n\nexport type ServerCapabilities = z.infer<typeof ServerCapabilitiesSchema>;\nexport const ClientCapabilitiesSchema = z\n  .object({\n    elicitation: z.optional(ElicitationCapabilitySchema),\n  })\n  .loose();\n\nexport type ClientCapabilities = z.infer<typeof ClientCapabilitiesSchema>;\nexport type ElicitationCapability = z.infer<typeof ElicitationCapabilitySchema>;\n\nexport const InitializeResultSchema = ResultSchema.extend({\n  protocolVersion: z.string(),\n  capabilities: ServerCapabilitiesSchema,\n  serverInfo: ClientOrServerImplementationSchema,\n  instructions: z.optional(z.string()),\n});\nexport type InitializeResult = z.infer<typeof InitializeResultSchema>;\n\nexport type PaginatedRequest = Request & {\n  params?: BaseParams & {\n    cursor?: string;\n  };\n};\n\nconst PaginatedResultSchema = ResultSchema.extend({\n  nextCursor: z.optional(z.string()),\n});\n\nconst ToolSchema = z\n  .object({\n    name: z.string(),\n    /**\n     * @see https://modelcontextprotocol.io/specification/2025-11-25/server/tools#tool\n     */\n    title: z.optional(z.string()),\n    description: z.optional(z.string()),\n    inputSchema: z\n      .object({\n        type: z.literal('object'),\n        properties: z.optional(z.object({}).loose()),\n      })\n      .loose(),\n    /**\n     * @see https://modelcontextprotocol.io/specification/2025-06-18/server/tools#output-schema\n     */\n    outputSchema: z.optional(z.object({}).loose()),\n    annotations: z.optional(\n      z\n        .object({\n          title: z.optional(z.string()),\n        })\n        .loose(),\n    ),\n    _meta: ToolMetaSchema,\n  })\n  .loose();\nexport type MCPTool = z.infer<typeof ToolSchema>;\nexport const ListToolsResultSchema = PaginatedResultSchema.extend({\n  tools: z.array(ToolSchema),\n});\nexport type ListToolsResult = z.infer<typeof ListToolsResultSchema>;\n\nconst TextContentSchema = z\n  .object({\n    type: z.literal('text'),\n    text: z.string(),\n  })\n  .loose();\nconst ImageContentSchema = z\n  .object({\n    type: z.literal('image'),\n    data: z.base64(),\n    mimeType: z.string(),\n  })\n  .loose();\nexport const ResourceSchema = z\n  .object({\n    uri: z.string(),\n    name: z.string(),\n    title: z.optional(z.string()),\n    description: z.optional(z.string()),\n    mimeType: z.optional(z.string()),\n    size: z.optional(z.number()),\n  })\n  .loose();\nexport type MCPResource = z.infer<typeof ResourceSchema>;\n\nexport const ListResourcesResultSchema = PaginatedResultSchema.extend({\n  resources: z.array(ResourceSchema),\n});\nexport type ListResourcesResult = z.infer<typeof ListResourcesResultSchema>;\n\nconst ResourceContentsSchema = z\n  .object({\n    /**\n     * The URI of this resource.\n     */\n    uri: z.string(),\n    /**\n     * Optional display name of the resource content.\n     */\n    name: z.optional(z.string()),\n    /**\n     * Optional human readable title.\n     */\n    title: z.optional(z.string()),\n    /**\n     * The MIME type of this resource, if known.\n     */\n    mimeType: z.optional(z.string()),\n  })\n  .loose();\nconst TextResourceContentsSchema = ResourceContentsSchema.extend({\n  text: z.string(),\n});\nconst BlobResourceContentsSchema = ResourceContentsSchema.extend({\n  blob: z.base64(),\n});\nconst EmbeddedResourceSchema = z\n  .object({\n    type: z.literal('resource'),\n    resource: z.union([TextResourceContentsSchema, BlobResourceContentsSchema]),\n  })\n  .loose();\nconst ResourceLinkContentSchema = z\n  .object({\n    type: z.literal('resource_link'),\n    uri: z.string(),\n    name: z.string(),\n    description: z.optional(z.string()),\n    mimeType: z.optional(z.string()),\n  })\n  .loose();\n\nexport const CallToolResultSchema = ResultSchema.extend({\n  content: z.array(\n    z.union([\n      TextContentSchema,\n      ImageContentSchema,\n      EmbeddedResourceSchema,\n      ResourceLinkContentSchema,\n    ]),\n  ),\n  /**\n   * @see https://modelcontextprotocol.io/specification/2025-06-18/server/tools#structured-content\n   */\n  structuredContent: z.optional(z.unknown()),\n  isError: z.boolean().default(false).optional(),\n}).or(\n  ResultSchema.extend({\n    toolResult: z.unknown(),\n  }),\n);\nexport type CallToolResult = z.infer<typeof CallToolResultSchema>;\n\nconst ResourceTemplateSchema = z\n  .object({\n    uriTemplate: z.string(),\n    name: z.string(),\n    title: z.optional(z.string()),\n    description: z.optional(z.string()),\n    mimeType: z.optional(z.string()),\n  })\n  .loose();\n\nexport const ListResourceTemplatesResultSchema = ResultSchema.extend({\n  resourceTemplates: z.array(ResourceTemplateSchema),\n});\nexport type ListResourceTemplatesResult = z.infer<\n  typeof ListResourceTemplatesResultSchema\n>;\n\nexport const ReadResourceResultSchema = ResultSchema.extend({\n  contents: z.array(\n    z.union([TextResourceContentsSchema, BlobResourceContentsSchema]),\n  ),\n});\nexport type ReadResourceResult = z.infer<typeof ReadResourceResultSchema>;\n\n// Completions\nconst PromptReferenceSchema = z\n  .object({\n    type: z.literal('ref/prompt'),\n    name: z.string(),\n  })\n  .loose();\n\nconst ResourceReferenceSchema = z\n  .object({\n    type: z.literal('ref/resource'),\n    uri: z.string(),\n  })\n  .loose();\n\nconst CompletionArgumentSchema = z\n  .object({\n    name: z.string(),\n    value: z.string(),\n  })\n  .loose();\n\nexport const CompleteRequestParamsSchema = BaseParamsSchema.extend({\n  ref: z.union([PromptReferenceSchema, ResourceReferenceSchema]),\n  argument: CompletionArgumentSchema,\n  context: z.optional(\n    z\n      .object({\n        arguments: z.record(z.string(), z.string()),\n      })\n      .loose(),\n  ),\n});\nexport type CompleteRequestParams = z.infer<typeof CompleteRequestParamsSchema>;\n\nexport const CompleteResultSchema = ResultSchema.extend({\n  completion: z\n    .object({\n      values: z.array(z.string()).max(100),\n      total: z.optional(z.number().int()),\n      hasMore: z.optional(z.boolean()),\n    })\n    .loose(),\n});\nexport type CompleteResult = z.infer<typeof CompleteResultSchema>;\n\n// Prompts\nconst PromptArgumentSchema = z\n  .object({\n    name: z.string(),\n    description: z.optional(z.string()),\n    required: z.optional(z.boolean()),\n  })\n  .loose();\n\nexport const PromptSchema = z\n  .object({\n    name: z.string(),\n    title: z.optional(z.string()),\n    description: z.optional(z.string()),\n    arguments: z.optional(z.array(PromptArgumentSchema)),\n  })\n  .loose();\nexport type MCPPrompt = z.infer<typeof PromptSchema>;\n\nexport const ListPromptsResultSchema = PaginatedResultSchema.extend({\n  prompts: z.array(PromptSchema),\n});\nexport type ListPromptsResult = z.infer<typeof ListPromptsResultSchema>;\n\nconst PromptMessageSchema = z\n  .object({\n    role: z.union([z.literal('user'), z.literal('assistant')]),\n    content: z.union([\n      TextContentSchema,\n      ImageContentSchema,\n      EmbeddedResourceSchema,\n      ResourceLinkContentSchema,\n    ]),\n  })\n  .loose();\nexport type MCPPromptMessage = z.infer<typeof PromptMessageSchema>;\n\nexport const GetPromptResultSchema = ResultSchema.extend({\n  description: z.optional(z.string()),\n  messages: z.array(PromptMessageSchema),\n});\nexport type GetPromptResult = z.infer<typeof GetPromptResultSchema>;\n\nconst ElicitationRequestParamsSchema = BaseParamsSchema.extend({\n  message: z.string(),\n  requestedSchema: z.unknown(),\n});\n\nexport const ElicitationRequestSchema = RequestSchema.extend({\n  method: z.literal('elicitation/create'),\n  params: ElicitationRequestParamsSchema,\n});\n\nexport type ElicitationRequest = z.infer<typeof ElicitationRequestSchema>;\n\nexport const ElicitResultSchema = ResultSchema.extend({\n  action: z.union([\n    z.literal('accept'),\n    z.literal('decline'),\n    z.literal('cancel'),\n  ]),\n  content: z.optional(z.record(z.string(), z.unknown())),\n});\n\nexport type ElicitResult = z.infer<typeof ElicitResultSchema>;\n","import { AISDKError } from '@ai-sdk/provider';\n\nconst name = 'AI_MCPClientError';\nconst marker = `vercel.ai.error.${name}`;\nconst symbol = Symbol.for(marker);\n\n/**\n * An error occurred with the MCP client.\n */\nexport class MCPClientError extends AISDKError {\n  private readonly [symbol] = true;\n  readonly data?: unknown;\n\n  /**\n   * JSON-RPC error code from the server response, per the JSON-RPC 2.0\n   * spec (e.g. `-32601` method-not-found, `-32602` invalid-params, or\n   * MCP-specific codes such as `-32002` resource-not-found). This is the\n   * application-level error code populated from `error.code` in the\n   * server's JSON-RPC error payload. Distinct from `statusCode`, which\n   * is the HTTP transport status.\n   */\n  readonly code?: number;\n\n  /**\n   * HTTP status code from the failed response, when the error originated\n   * from the streamable HTTP transport. Undefined for stdio transport\n   * errors and for failures that do not have an associated response\n   * status (e.g. network errors, abort). Distinct from `code`, which is\n   * the JSON-RPC application error code.\n   */\n  readonly statusCode?: number;\n\n  /**\n   * URL of the MCP endpoint the failing request was sent to, when the\n   * error originated from an HTTP transport failure.\n   */\n  readonly url?: string;\n\n  /**\n   * Body of the failing HTTP response, decoded as text, when available.\n   * Undefined when the body could not be read or the error did not have\n   * an associated response.\n   */\n  readonly responseBody?: string;\n\n  constructor({\n    name = 'MCPClientError',\n    message,\n    cause,\n    data,\n    code,\n    statusCode,\n    url,\n    responseBody,\n  }: {\n    name?: string;\n    message: string;\n    cause?: unknown;\n    data?: unknown;\n    code?: number;\n    statusCode?: number;\n    url?: string;\n    responseBody?: string;\n  }) {\n    super({ name, message, cause });\n    this.data = data;\n    this.code = code;\n    this.statusCode = statusCode;\n    this.url = url;\n    this.responseBody = responseBody;\n  }\n\n  static isInstance(error: unknown): error is MCPClientError {\n    return AISDKError.hasMarker(error, marker);\n  }\n}\n","import { spawn, type ChildProcess } from 'node:child_process';\nimport { getEnvironment } from './get-environment';\nimport type { StdioConfig } from './mcp-stdio-transport';\n\nexport function createChildProcess(\n  config: StdioConfig,\n  signal: AbortSignal,\n): ChildProcess {\n  return spawn(config.command, config.args ?? [], {\n    env: getEnvironment(config.env),\n    stdio: ['pipe', 'pipe', config.stderr ?? 'inherit'],\n    shell: false,\n    signal,\n    windowsHide: globalThis.process.platform === 'win32' && isElectron(),\n    cwd: config.cwd,\n  });\n}\n\nfunction isElectron() {\n  return 'type' in globalThis.process;\n}\n","/**\n * Constructs the environment variables for the child process.\n *\n * @param customEnv - Custom environment variables to merge with default environment variables.\n * @returns The environment variables for the child process.\n */\nexport function getEnvironment(\n  customEnv?: Record<string, string>,\n): Record<string, string> {\n  const DEFAULT_INHERITED_ENV_VARS =\n    globalThis.process.platform === 'win32'\n      ? [\n          'APPDATA',\n          'HOMEDRIVE',\n          'HOMEPATH',\n          'LOCALAPPDATA',\n          'PATH',\n          'PROCESSOR_ARCHITECTURE',\n          'SYSTEMDRIVE',\n          'SYSTEMROOT',\n          'TEMP',\n          'USERNAME',\n          'USERPROFILE',\n        ]\n      : ['HOME', 'LOGNAME', 'PATH', 'SHELL', 'TERM', 'USER'];\n\n  const env: Record<string, string> = customEnv ? { ...customEnv } : {};\n\n  for (const key of DEFAULT_INHERITED_ENV_VARS) {\n    const value = globalThis.process.env[key];\n    if (value === undefined) {\n      continue;\n    }\n\n    if (value.startsWith('()')) {\n      continue;\n    }\n\n    env[key] = value;\n  }\n\n  return env;\n}\n","import type { ChildProcess, IOType } from 'node:child_process';\nimport type { Stream } from 'node:stream';\nimport { parseJSONRPCMessage, type JSONRPCMessage } from '../json-rpc-message';\nimport type { MCPTransport } from '../mcp-transport';\nimport { MCPClientError } from '../../error/mcp-client-error';\nimport { createChildProcess } from './create-child-process';\n\nexport interface StdioConfig {\n  command: string;\n  args?: string[];\n  env?: Record<string, string>;\n  stderr?: IOType | Stream | number;\n  cwd?: string;\n}\n\nexport class StdioMCPTransport implements MCPTransport {\n  private process?: ChildProcess;\n  private abortController: AbortController = new AbortController();\n  private readBuffer: ReadBuffer = new ReadBuffer();\n  private serverParams: StdioConfig;\n\n  onclose?: () => void;\n  onerror?: (error: unknown) => void;\n  onmessage?: (message: JSONRPCMessage) => void;\n\n  constructor(server: StdioConfig) {\n    this.serverParams = server;\n  }\n\n  async start(): Promise<void> {\n    if (this.process) {\n      throw new MCPClientError({\n        message: 'StdioMCPTransport already started.',\n      });\n    }\n\n    return new Promise((resolve, reject) => {\n      try {\n        const process = createChildProcess(\n          this.serverParams,\n          this.abortController.signal,\n        );\n\n        this.process = process;\n\n        this.process.on('error', error => {\n          if (error.name === 'AbortError') {\n            this.onclose?.();\n            return;\n          }\n\n          reject(error);\n          this.onerror?.(error);\n        });\n\n        this.process.on('spawn', () => {\n          resolve();\n        });\n\n        this.process.on('close', _code => {\n          this.process = undefined;\n          this.onclose?.();\n        });\n\n        this.process.stdin?.on('error', error => {\n          this.onerror?.(error);\n        });\n\n        this.process.stdout?.on('data', chunk => {\n          this.readBuffer.append(chunk);\n          void this.processReadBuffer();\n        });\n\n        this.process.stdout?.on('error', error => {\n          this.onerror?.(error);\n        });\n      } catch (error) {\n        reject(error);\n        this.onerror?.(error);\n      }\n    });\n  }\n\n  private async processReadBuffer() {\n    while (true) {\n      const line = this.readBuffer.readLine();\n      if (line === null) {\n        break;\n      }\n\n      try {\n        const message = await deserializeMessage(line);\n        this.onmessage?.(message);\n      } catch (error) {\n        this.onerror?.(error as Error);\n      }\n    }\n  }\n\n  async close(): Promise<void> {\n    this.abortController.abort();\n    this.process = undefined;\n    this.readBuffer.clear();\n  }\n\n  send(message: JSONRPCMessage): Promise<void> {\n    return new Promise(resolve => {\n      if (!this.process?.stdin) {\n        throw new MCPClientError({\n          message: 'StdioClientTransport not connected',\n        });\n      }\n\n      const json = serializeMessage(message);\n      if (this.process.stdin.write(json)) {\n        resolve();\n      } else {\n        this.process.stdin.once('drain', resolve);\n      }\n    });\n  }\n}\n\nclass ReadBuffer {\n  private buffer?: Buffer;\n\n  append(chunk: Buffer): void {\n    this.buffer = this.buffer ? Buffer.concat([this.buffer, chunk]) : chunk;\n  }\n\n  readLine(): string | null {\n    if (!this.buffer) return null;\n\n    const index = this.buffer.indexOf('\\n');\n    if (index === -1) {\n      return null;\n    }\n\n    const line = this.buffer.toString('utf8', 0, index);\n    this.buffer = this.buffer.subarray(index + 1);\n    return line;\n  }\n\n  clear(): void {\n    this.buffer = undefined;\n  }\n}\n\nfunction serializeMessage(message: JSONRPCMessage): string {\n  return JSON.stringify(message) + '\\n';\n}\n\nexport async function deserializeMessage(\n  line: string,\n): Promise<JSONRPCMessage> {\n  return 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/**\n     * Optional display name of the resource content.\n     */\n    name: z.optional(z.string()),\n    /**\n     * Optional human readable title.\n     */\n    title: z.optional(z.string()),\n    /**\n     * The MIME type of this resource, if known.\n     */\n    mimeType: z.optional(z.string()),\n  })\n  .loose();\nconst TextResourceContentsSchema = ResourceContentsSchema.extend({\n  text: z.string(),\n});\nconst BlobResourceContentsSchema = ResourceContentsSchema.extend({\n  blob: z.base64(),\n});\nconst EmbeddedResourceSchema = z\n  .object({\n    type: z.literal('resource'),\n    resource: z.union([TextResourceContentsSchema, BlobResourceContentsSchema]),\n  })\n  .loose();\nconst ResourceLinkContentSchema = z\n  .object({\n    type: z.literal('resource_link'),\n    uri: z.string(),\n    name: z.string(),\n    description: z.optional(z.string()),\n    mimeType: z.optional(z.string()),\n  })\n  .loose();\n\nexport const CallToolResultSchema = ResultSchema.extend({\n  content: 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This is the\n   * application-level error code populated from `error.code` in the\n   * server's JSON-RPC error payload. Distinct from `statusCode`, which\n   * is the HTTP transport status.\n   */\n  readonly code?: number;\n\n  /**\n   * HTTP status code from the failed response, when the error originated\n   * from the streamable HTTP transport. Undefined for stdio transport\n   * errors and for failures that do not have an associated response\n   * status (e.g. network errors, abort). 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[], {\n    env: getEnvironment(config.env),\n    stdio: ['pipe', 'pipe', config.stderr ?? 'inherit'],\n    shell: false,\n    signal,\n    windowsHide: globalThis.process.platform === 'win32' && isElectron(),\n    cwd: config.cwd,\n  });\n}\n\nfunction isElectron() {\n  return 'type' in globalThis.process;\n}\n","/**\n * Constructs the environment variables for the child process.\n *\n * @param customEnv - Custom environment variables to merge with default environment variables.\n * @returns The environment variables for the child process.\n */\nexport function getEnvironment(\n  customEnv?: Record<string, string>,\n): Record<string, string> {\n  const DEFAULT_INHERITED_ENV_VARS =\n    globalThis.process.platform === 'win32'\n      ? 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package.json

 {
   "name": "@ai-sdk/mcp",
-  "version": "2.0.32",
+  "version": "2.0.33",
   "type": "module",
@@ -35,4 +35,4 @@ "license": "Apache-2.0",
     "pkce-challenge": "^5.0.1",
-    "@ai-sdk/provider-utils": "5.0.27",
-    "@ai-sdk/provider": "4.0.7"
+    "@ai-sdk/provider": "4.0.7",
+    "@ai-sdk/provider-utils": "5.0.27"
   },
@@ -39,0 +39,0 @@ "devDependencies": {

README.md

@@ -62,2 +62,13 @@ # AI SDK - Model Context Protocol Client
 
+## Protocol versions
+
+The client supports legacy MCP protocol versions through the `initialize`
+handshake and MCP `2026-07-28` through stateless protocol discovery. The
+built-in stdio transport probes with `server/discover` and falls back to the
+legacy handshake when connected to an older server.
+
+Custom transports can opt into the same negotiation by setting
+`supportsProtocolVersionDiscovery` to `true`. Modern requests include the
+protocol version, client capabilities, and client information in `_meta`.
+
 For streaming responses, close the MCP client when the stream finishes:
@@ -94,2 +105,6 @@
 
+Session persistence applies only to legacy MCP protocol versions. MCP
+`2026-07-28` is stateless and does not use session ids or cached initialize
+results.
+
 ```ts
@@ -96,0 +111,0 @@ import { createMCPClient } from '@ai-sdk/mcp';

src/tool/json-rpc-message.ts

@@ -30,3 +30,3 @@ import { parseJSON } from '@ai-sdk/provider-utils';
     jsonrpc: z.literal(JSONRPC_VERSION),
-    id: z.union([z.string(), z.number().int()]),
+    id: z.optional(z.union([z.string(), z.number().int()])),
     error: z.object({
@@ -33,0 +33,0 @@ code: z.number().int(),

src/tool/mcp-client.ts

@@ -29,10 +29,18 @@ import type { JSONObject, JSONSchema7, JSONValue } from '@ai-sdk/provider';
   type MCPTransportConfig,
+  type MCPTransportSendOptions,
 } from './mcp-transport';
 import { getMCPAppToolMeta, MCP_APP_MIME_TYPE } from './mcp-apps';
 import {
+  createMCPToolHeaders,
+  getMCPToolHeaderBindings,
+  type MCPToolHeaderBinding,
+} from './mcp-http-headers';
+import {
   CallToolResultSchema,
   CompleteResultSchema,
+  DiscoverResultSchema,
   ElicitationRequestSchema,
   ElicitResultSchema,
   InitializeResultSchema,
+  LATEST_LEGACY_PROTOCOL_VERSION,
   LATEST_PROTOCOL_VERSION,
@@ -70,5 +78,8 @@ ListResourceTemplatesResultSchema,
   type InitializeResult,
+  type DiscoverResult,
 } from './types';
 const CLIENT_VERSION = '1.0.0';
 const DEFAULT_MAX_TOOL_CALL_RETRIES = 0;
+const DEFAULT_PROTOCOL_DISCOVERY_TIMEOUT = 1000;
+const MODERN_PROTOCOL_ERROR_CODES = [-32020, -32021, -32022];
 
@@ -236,2 +247,12 @@ const DEFAULT_RETRY_ERROR_CODES = [
   /**
+   * Whether transports that support stateless protocol discovery should probe
+   * with `server/discover` before falling back to legacy initialization.
+   *
+   * Disable this for legacy servers that require `initialize` to be the first
+   * request.
+   *
+   * @default true
+   */
+  protocolVersionDiscovery?: boolean;
+  /**
    * Options that bound or cancel transport startup and the initialize request.
@@ -394,2 +415,3 @@ */
   private transport: MCPTransport;
+  private protocolVersionDiscovery: boolean;
   private onUncaughtError?: (error: unknown) => void;
@@ -409,3 +431,3 @@ private maxRetries: number;
   private _initializeResult: InitializeResult = {
-    protocolVersion: LATEST_PROTOCOL_VERSION,
+    protocolVersion: LATEST_LEGACY_PROTOCOL_VERSION,
     capabilities: {},
@@ -415,2 +437,5 @@ serverInfo: this._serverInfo,
   private _serverInstructions?: string;
+  private protocolEra: 'legacy' | 'modern' = 'legacy';
+  private protocolVersion = LATEST_LEGACY_PROTOCOL_VERSION;
+  private toolHeaderBindings = new Map<string, MCPToolHeaderBinding[]>();
   private isClosed = true;
@@ -431,2 +456,3 @@ private elicitationRequestHandler?: (
     initializationOptions,
+    protocolVersionDiscovery = true,
   }: MCPClientConfig) {
@@ -438,2 +464,3 @@ this.onUncaughtError = onUncaughtError;
     this.initializationOptions = initializationOptions;
+    this.protocolVersionDiscovery = protocolVersionDiscovery;
 
@@ -521,2 +548,16 @@ if (isCustomMcpTransport(transportConfig)) {
 
+      if (
+        this.protocolVersionDiscovery &&
+        this.transport.supportsProtocolVersionDiscovery
+      ) {
+        const discovered = await this.tryProtocolDiscovery(signal);
+        if (discovered) {
+          return this;
+        }
+      }
+
+      this.protocolEra = 'legacy';
+      this.protocolVersion = LATEST_LEGACY_PROTOCOL_VERSION;
+      this.setTransportProtocolVersion(this.protocolVersion);
+
       const result = await this.request({
@@ -526,3 +567,3 @@ request: {
           params: {
-            protocolVersion: LATEST_PROTOCOL_VERSION,
+            protocolVersion: LATEST_LEGACY_PROTOCOL_VERSION,
             capabilities: this.clientCapabilities,
@@ -578,2 +619,71 @@ clientInfo: this.clientInfo,
 
+  private async tryProtocolDiscovery(
+    signal: AbortSignal | undefined,
+  ): Promise<boolean> {
+    this.protocolEra = 'modern';
+    this.protocolVersion = LATEST_PROTOCOL_VERSION;
+    this.setTransportProtocolVersion(this.protocolVersion);
+
+    try {
+      const result = await this.request({
+        request: { method: 'server/discover' },
+        resultSchema: DiscoverResultSchema,
+        options: {
+          signal,
+          timeout: DEFAULT_PROTOCOL_DISCOVERY_TIMEOUT,
+        },
+      });
+
+      this.applyDiscoverResult(result);
+      return true;
+    } catch (error) {
+      if (
+        MCPClientError.isInstance(error) &&
+        error.code != null &&
+        MODERN_PROTOCOL_ERROR_CODES.includes(error.code)
+      ) {
+        throw error;
+      }
+
+      return false;
+    }
+  }
+
+  private applyDiscoverResult(result: DiscoverResult): void {
+    if (!result.supportedVersions.includes(this.protocolVersion)) {
+      throw new MCPClientError({
+        message: `Server does not support the requested protocol version: ${this.protocolVersion}`,
+      });
+    }
+
+    const serverInfo = result._meta?.['io.modelcontextprotocol/serverInfo'];
+    if (
+      serverInfo != null &&
+      typeof serverInfo === 'object' &&
+      'name' in serverInfo &&
+      typeof serverInfo.name === 'string' &&
+      'version' in serverInfo &&
+      typeof serverInfo.version === 'string'
+    ) {
+      this._serverInfo = serverInfo as Configuration;
+    }
+
+    this.serverCapabilities = result.capabilities;
+    this._serverInstructions = result.instructions;
+    this._initializeResult = {
+      protocolVersion: this.protocolVersion,
+      capabilities: result.capabilities,
+      serverInfo: this._serverInfo,
+      instructions: result.instructions,
+    };
+  }
+
+  private setTransportProtocolVersion(version: string): void {
+    if (this.transport.setProtocolVersion) {
+      this.transport.setProtocolVersion(version);
+    } else {
+      this.transport.protocolVersion = version;
+    }
+  }
+
   private applyInitializeResult(result: InitializeResult): void {
@@ -587,9 +697,7 @@ if (!SUPPORTED_PROTOCOL_VERSIONS.includes(result.protocolVersion)) {
     this.serverCapabilities = result.capabilities;
+    this.protocolEra = 'legacy';
+    this.protocolVersion = result.protocolVersion;
     this._serverInfo = result.serverInfo;
     this._initializeResult = result;
-    if (this.transport.setProtocolVersion) {
-      this.transport.setProtocolVersion(result.protocolVersion);
-    } else {
-      this.transport.protocolVersion = result.protocolVersion;
-    }
+    this.setTransportProtocolVersion(result.protocolVersion);
     this._serverInstructions = result.instructions;
@@ -606,8 +714,7 @@ }
     message: JSONRPCMessage,
-    signal: AbortSignal | undefined,
+    options?: MCPTransportSendOptions,
   ): Promise<void> {
-    return this.transport.send(
-      message,
-      signal == null ? undefined : { signal },
-    );
+    return options == null
+      ? this.transport.send(message)
+      : this.transport.send(message, options);
   }
@@ -618,2 +725,3 @@
       case 'initialize':
+      case 'server/discover':
         break;
@@ -694,7 +802,25 @@ case 'completion/complete':
       const messageId = this.requestMessageId++;
+      const preparedRequest =
+        this.protocolEra === 'modern'
+          ? {
+              ...request,
+              params: {
+                ...request.params,
+                _meta: {
+                  ...request.params?._meta,
+                  'io.modelcontextprotocol/protocolVersion':
+                    this.protocolVersion,
+                  'io.modelcontextprotocol/clientCapabilities':
+                    this.clientCapabilities,
+                  'io.modelcontextprotocol/clientInfo': this.clientInfo,
+                },
+              },
+            }
+          : request;
       const jsonrpcRequest: JSONRPCRequest = {
-        ...request,
+        ...preparedRequest,
         jsonrpc: '2.0',
         id: messageId,
       };
+      const headers = this.getToolRequestHeaders(preparedRequest);
 
@@ -747,2 +873,17 @@ const rejectWithAbortError = () => {
         try {
+          if (
+            this.protocolEra === 'modern' &&
+            response.result.resultType == null
+          ) {
+            throw new MCPClientError({
+              message: 'Modern MCP result is missing resultType',
+            });
+          }
+          if (response.result.resultType === 'input_required') {
+            throw new MCPClientError({
+              message:
+                'Server requested additional input, but multi round-trip requests are not supported yet',
+            });
+          }
+
           const result = resultSchema.parse(response.result);
@@ -752,6 +893,8 @@ cleanup();
         } catch (error) {
-          const parseError = new MCPClientError({
-            message: 'Failed to parse server response',
-            cause: error,
-          });
+          const parseError = MCPClientError.isInstance(error)
+            ? error
+            : new MCPClientError({
+                message: 'Failed to parse server response',
+                cause: error,
+              });
           rejectAndCleanup(parseError);
@@ -767,6 +910,10 @@ }
 
+      const sendOptions: MCPTransportSendOptions = {
+        ...(transportSignal == null ? {} : { signal: transportSignal }),
+        ...(headers == null ? {} : { headers }),
+      };
       const sendPromise =
-        transportSignal == null
-          ? this.transport.send(jsonrpcRequest)
-          : this.send(jsonrpcRequest, transportSignal);
+        Object.keys(sendOptions).length === 0
+          ? this.send(jsonrpcRequest)
+          : this.send(jsonrpcRequest, sendOptions);
 
@@ -786,3 +933,3 @@ sendPromise.catch(error => {
   } = {}): Promise<ListToolsResult> {
-    return this.request({
+    const result = await this.request({
       request: { method: 'tools/list', params },
@@ -792,4 +939,71 @@ resultSchema: ListToolsResultSchema,
     });
+    return this.prepareToolDefinitions(result, params?.cursor == null);
   }
 
+  private prepareToolDefinitions(
+    definitions: ListToolsResult,
+    resetHeaderBindings = false,
+  ): ListToolsResult {
+    if (
+      this.protocolEra !== 'modern' ||
+      !this.transport.supportsMcpToolParameterHeaders
+    ) {
+      return definitions;
+    }
+
+    if (resetHeaderBindings) {
+      this.toolHeaderBindings.clear();
+    }
+    const tools = definitions.tools.filter(toolDefinition => {
+      const result = getMCPToolHeaderBindings(toolDefinition.inputSchema);
+      if (!result.success) {
+        this.onError(
+          new MCPClientError({
+            message: `Ignoring MCP tool "${toolDefinition.name}": ${result.error}`,
+          }),
+        );
+        return false;
+      }
+
+      this.toolHeaderBindings.set(toolDefinition.name, result.bindings);
+      return true;
+    });
+
+    return { ...definitions, tools };
+  }
+
+  private getToolRequestHeaders(
+    request: Request,
+  ): Record<string, string> | undefined {
+    if (
+      this.protocolEra !== 'modern' ||
+      request.method !== 'tools/call' ||
+      typeof request.params?.name !== 'string'
+    ) {
+      return undefined;
+    }
+
+    const bindings = this.toolHeaderBindings.get(request.params.name);
+    if (bindings == null || bindings.length === 0) {
+      return undefined;
+    }
+
+    const args = request.params.arguments;
+    if (args == null || typeof args !== 'object' || Array.isArray(args)) {
+      return undefined;
+    }
+
+    try {
+      return createMCPToolHeaders({
+        bindings,
+        args: args as Record<string, unknown>,
+      });
+    } catch (error) {
+      throw new MCPClientError({
+        message: `Failed to create MCP headers for tool "${request.params.name}"`,
+        cause: error,
+      });
+    }
+  }
+
   private async callToolWithRetry({
@@ -957,3 +1171,6 @@ options,
     await waitForAbort(
-      this.send(jsonrpcNotification, options?.signal),
+      this.send(
+        jsonrpcNotification,
+        options?.signal == null ? undefined : { signal: options.signal },
+      ),
       options?.signal,
@@ -988,2 +1205,3 @@ );
   ): McpToolSet<TOOL_SCHEMAS> {
+    definitions = this.prepareToolDefinitions(definitions);
     const tools: Record<string, Tool & { _meta?: ToolMeta }> = {};
@@ -1303,2 +1521,13 @@
   private onResponse(response: JSONRPCResponse | JSONRPCError): void {
+    if (response.id == null) {
+      this.onError(
+        new MCPClientError({
+          message: `Protocol error: Received a response without a message ID: ${JSON.stringify(
+            response,
+          )}`,
+        }),
+      );
+      return;
+    }
+
     const messageId = Number(response.id);
@@ -1305,0 +1534,0 @@ const handler = this.responseHandlers.get(messageId);

src/tool/mcp-http-transport.ts

@@ -13,3 +13,3 @@ import {
 } from './json-rpc-message';
-import type { MCPTransport } from './mcp-transport';
+import type { MCPTransport, MCPTransportSendOptions } from './mcp-transport';
 import { VERSION } from '../version';
@@ -23,3 +23,7 @@ import {
 } from './oauth';
-import { LATEST_PROTOCOL_VERSION } from './types';
+import {
+  LATEST_LEGACY_PROTOCOL_VERSION,
+  LATEST_PROTOCOL_VERSION,
+} from './types';
+import { encodeMCPHeaderValue } from './mcp-http-headers';
 
@@ -38,2 +42,4 @@ function isMessageEvent(event: string | undefined): boolean {
 export class HttpMCPTransport implements MCPTransport {
+  readonly supportsProtocolVersionDiscovery = true;
+  readonly supportsMcpToolParameterHeaders = true;
   private url: URL;
@@ -96,3 +102,4 @@ private abortController?: AbortController;
     this.sessionId = initialSessionId;
-    this.protocolVersion = initialProtocolVersion;
+    this.protocolVersion =
+      initialProtocolVersion ?? LATEST_LEGACY_PROTOCOL_VERSION;
     this.onSessionIdChange = onSessionIdChange;
@@ -106,4 +113,25 @@ this.onSessionExpired = onSessionExpired;
     this.protocolVersion = version;
+
+    if (!this.abortController) {
+      return;
+    }
+
+    if (this.isModernProtocol()) {
+      this.inboundSseConnection?.close();
+      this.inboundSseConnection = undefined;
+      return;
+    }
+
+    if (!this.inboundSseConnection) {
+      this.startInboundSse();
+    }
   }
 
+  private isModernProtocol(): boolean {
+    return (
+      (this.protocolVersion ?? LATEST_PROTOCOL_VERSION) ===
+      LATEST_PROTOCOL_VERSION
+    );
+  }
+
   private async commonHeaders({
@@ -119,6 +147,7 @@ base,
       ...base,
-      'mcp-protocol-version': this.protocolVersion ?? LATEST_PROTOCOL_VERSION,
+      'mcp-protocol-version':
+        this.protocolVersion ?? LATEST_LEGACY_PROTOCOL_VERSION,
     };
 
-    if (includeSessionId && this.sessionId) {
+    if (!this.isModernProtocol() && includeSessionId && this.sessionId) {
       headers['mcp-session-id'] = this.sessionId;
@@ -151,2 +180,6 @@ }
   private applySessionIdFromResponse(response: Response): void {
+    if (this.isModernProtocol()) {
+      return;
+    }
+
     const sessionId = response.headers.get('mcp-session-id');
@@ -200,3 +233,8 @@ if (sessionId) {
 
-    this.startInboundSse();
+    if (
+      this.protocolVersion != null &&
+      this.protocolVersion !== LATEST_PROTOCOL_VERSION
+    ) {
+      this.startInboundSse();
+    }
   }
@@ -210,2 +248,3 @@
       if (
+        !this.isModernProtocol() &&
         this.sessionId &&
@@ -232,3 +271,3 @@ this.terminateSessionOnClose &&
     message: JSONRPCMessage,
-    options?: { signal?: AbortSignal },
+    options?: MCPTransportSendOptions,
   ): Promise<void> {
@@ -256,2 +295,8 @@ options?.signal?.throwIfAborted();
             Accept: 'application/json, text/event-stream',
+            ...(this.isModernProtocol() ? options?.headers : {}),
+            ...(this.isModernProtocol() &&
+            'method' in message &&
+            'id' in message
+              ? this.getStandardRequestHeaders(message)
+              : {}),
           },
@@ -297,3 +342,3 @@ includeSessionId: !isInitializeRequest,
           // Do not await to avoid blocking send()
-          if (!this.inboundSseConnection) {
+          if (!this.isModernProtocol() && !this.inboundSseConnection) {
             this.startInboundSse();
@@ -306,6 +351,21 @@ }
           const text = await response.text().catch(() => null);
+
+          if ('id' in message && text != null) {
+            const jsonRpcMessage = await parseJSONRPCMessage(text).catch(
+              () => undefined,
+            );
+            if (jsonRpcMessage != null && 'error' in jsonRpcMessage) {
+              this.onmessage?.(
+                jsonRpcMessage.id == null
+                  ? { ...jsonRpcMessage, id: message.id }
+                  : jsonRpcMessage,
+              );
+              return;
+            }
+          }
+
           let errorMessage = `MCP HTTP Transport Error: POSTing to endpoint (HTTP ${response.status}): ${text}`;
 
           if (response.status === 404) {
-            if (sessionIdForRequest) {
+            if (!this.isModernProtocol() && sessionIdForRequest) {
               this.expireSessionId(sessionIdForRequest);
@@ -315,3 +375,3 @@
                 '. The MCP session expired. Create a new client without `initialSessionId` to start a fresh session';
-            } else {
+            } else if (!this.isModernProtocol()) {
               errorMessage +=
@@ -430,2 +490,23 @@ '. This server does not support HTTP transport. Try using `sse` transport instead';
 
+  private getStandardRequestHeaders(
+    message: Extract<JSONRPCMessage, { method: string; id: unknown }>,
+  ): Record<string, string> {
+    const headers: Record<string, string> = {
+      'Mcp-Method': message.method,
+    };
+    const params = message.params;
+    const name =
+      message.method === 'resources/read'
+        ? params?.uri
+        : message.method === 'tools/call' || message.method === 'prompts/get'
+          ? params?.name
+          : undefined;
+
+    if (typeof name === 'string') {
+      headers['Mcp-Name'] = encodeMCPHeaderValue(name);
+    }
+
+    return headers;
+  }
+
   private getNextReconnectionDelay(attempt: number): number {
@@ -466,2 +547,6 @@ const {
   ): void {
+    if (this.isModernProtocol()) {
+      return;
+    }
+
     void this.openInboundSse(triedAuth, resumeToken).catch(error => {
@@ -480,2 +565,6 @@ if (error instanceof Error && error.name === 'AbortError') {
   ): Promise<void> {
+    if (this.isModernProtocol()) {
+      return;
+    }
+
     try {
@@ -482,0 +571,0 @@ const sessionIdForRequest = this.sessionId;

src/tool/mcp-sse-transport.ts

@@ -17,3 +17,3 @@ import {
 } from './oauth';
-import { LATEST_PROTOCOL_VERSION } from './types';
+import { LATEST_LEGACY_PROTOCOL_VERSION } from './types';
 
@@ -73,3 +73,4 @@ function isMessageEvent(event: string | undefined): boolean {
       ...base,
-      'mcp-protocol-version': this.protocolVersion ?? LATEST_PROTOCOL_VERSION,
+      'mcp-protocol-version':
+        this.protocolVersion ?? LATEST_LEGACY_PROTOCOL_VERSION,
     };
@@ -76,0 +77,0 @@

src/tool/mcp-stdio/mcp-stdio-transport.ts

@@ -17,2 +17,3 @@ import type { ChildProcess, IOType } from 'node:child_process';
 export class StdioMCPTransport implements MCPTransport {
+  readonly supportsProtocolVersionDiscovery = true;
   private process?: ChildProcess;
@@ -19,0 +20,0 @@ private abortController: AbortController = new AbortController();

src/tool/mcp-transport.ts

@@ -7,2 +7,3 @@ import type { FetchFunction } from '@ai-sdk/provider-utils';
 import type { OAuthClientProvider } from './oauth';
+import { LATEST_PROTOCOL_VERSION } from './types';
 
@@ -20,2 +21,7 @@ /**
   /**
+   * Request-specific HTTP headers produced from MCP tool parameters.
+   */
+  headers?: Record<string, string>;
+
+  /**
    * Associates an outgoing message with an incoming request.
@@ -45,2 +51,16 @@ */
   /**
+   * Whether this transport can probe for stateless MCP protocol versions.
+   *
+   * Custom transports default to the legacy initialization flow unless they
+   * explicitly opt in.
+   */
+  supportsProtocolVersionDiscovery?: boolean;
+
+  /**
+   * Whether this transport mirrors x-mcp-header tool parameters into request
+   * headers.
+   */
+  supportsMcpToolParameterHeaders?: boolean;
+
+  /**
    * Initialize and start the transport
@@ -167,3 +187,7 @@ */
     case 'http':
-      return new HttpMCPTransport(config);
+      return new HttpMCPTransport({
+        ...config,
+        initialProtocolVersion:
+          config.initialProtocolVersion ?? LATEST_PROTOCOL_VERSION,
+      });
     default:
@@ -170,0 +194,0 @@ throw new MCPClientError({

src/tool/mock-mcp-transport.ts

@@ -5,3 +5,3 @@ import { delay } from '@ai-sdk/provider-utils';
 import {
-  LATEST_PROTOCOL_VERSION,
+  LATEST_LEGACY_PROTOCOL_VERSION,
   type MCPTool,
@@ -167,3 +167,3 @@ type MCPResource,
           result: this.initializeResult || {
-            protocolVersion: LATEST_PROTOCOL_VERSION,
+            protocolVersion: LATEST_LEGACY_PROTOCOL_VERSION,
             serverInfo: {
@@ -170,0 +170,0 @@ name: 'mock-mcp-server',

src/tool/oauth-types.ts

@@ -42,2 +42,3 @@ import { z } from 'zod/v4';
     refresh_token: z.string().optional(),
+    issuer: SafeUrlSchema.optional(),
     authorization_server: SafeUrlSchema.optional(),
@@ -70,2 +71,4 @@ token_endpoint: SafeUrlSchema.optional(),
   registration_endpoint: SafeUrlSchema.optional(),
+  authorization_response_iss_parameter_supported: z.boolean().optional(),
+  client_id_metadata_document_supported: z.boolean().optional(),
   scopes_supported: z.array(z.string()).optional(),
@@ -92,2 +95,4 @@ response_types_supported: z.array(z.string()),
   registration_endpoint: SafeUrlSchema.optional(),
+  authorization_response_iss_parameter_supported: z.boolean().optional(),
+  client_id_metadata_document_supported: z.boolean().optional(),
   scopes_supported: z.array(z.string()).optional(),
@@ -120,2 +125,3 @@ response_types_supported: z.array(z.string()),
     client_secret_expires_at: z.number().optional(),
+    issuer: SafeUrlSchema.optional(),
     authorization_server: SafeUrlSchema.optional(),
@@ -129,2 +135,5 @@ token_endpoint: SafeUrlSchema.optional(),
     redirect_uris: z.array(SafeUrlSchema),
+    application_type: z
+      .union([z.literal('native'), z.literal('web')])
+      .optional(),
     token_endpoint_auth_method: z.string().optional(),
@@ -131,0 +140,0 @@ grant_types: z.array(z.string()).optional(),

src/tool/oauth.ts

@@ -34,2 +34,3 @@ import pkceChallenge from 'pkce-challenge';
 export interface OAuthAuthorizationServerInformation {
+  issuer?: string;
   authorizationServerUrl: string;
@@ -126,2 +127,16 @@ tokenEndpoint: string;
 
+function validateAuthorizationResponseIssuer({
+  callbackIssuer,
+  expectedIssuer,
+}: {
+  callbackIssuer: string | undefined;
+  expectedIssuer: string;
+}): void {
+  if (callbackIssuer != null && callbackIssuer !== expectedIssuer) {
+    throw new MCPClientOAuthError({
+      message: `OAuth authorization response issuer ${callbackIssuer} does not match expected issuer ${expectedIssuer}`,
+    });
+  }
+}
+
 function createAuthorizationServerInformation(
@@ -132,2 +147,3 @@ authorizationServerUrl: string | URL,
   return {
+    issuer: metadata?.issuer ?? String(authorizationServerUrl),
     authorizationServerUrl: normalizeUrl(authorizationServerUrl),
@@ -148,2 +164,3 @@ tokenEndpoint: normalizeUrl(
     ...tokens,
+    issuer: authorizationServerInformation.issuer,
     authorization_server: authorizationServerInformation.authorizationServerUrl,
@@ -162,2 +179,3 @@ token_endpoint: authorizationServerInformation.tokenEndpoint,
     ...clientInformation,
+    issuer: authorizationServerInformation.issuer,
     authorization_server: authorizationServerInformation.authorizationServerUrl,
@@ -169,2 +187,3 @@ token_endpoint: authorizationServerInformation.tokenEndpoint,
 function getAuthorizationServerInformationFromCredentials(credentials?: {
+  issuer?: string;
   authorization_server?: string;
@@ -178,2 +197,3 @@ token_endpoint?: string;
   return {
+    issuer: credentials.issuer,
     authorizationServerUrl: normalizeUrl(credentials.authorization_server),
@@ -203,2 +223,3 @@ tokenEndpoint: normalizeUrl(credentials.token_endpoint),
     return {
+      issuer: providerAuthorizationServerInformation.issuer,
       authorizationServerUrl: normalizeUrl(
@@ -269,2 +290,6 @@ providerAuthorizationServerInformation.authorizationServerUrl,
   if (
+    (storedAuthorizationServerInformation.issuer != null &&
+      currentAuthorizationServerInformation.issuer != null &&
+      storedAuthorizationServerInformation.issuer !==
+        currentAuthorizationServerInformation.issuer) ||
     storedAuthorizationServerInformation.authorizationServerUrl !==
@@ -1062,2 +1087,5 @@ currentAuthorizationServerInformation.authorizationServerUrl ||
 
+  const applicationType =
+    clientMetadata.application_type ??
+    inferOAuthApplicationType(clientMetadata.redirect_uris);
   const response = await (fetchFn ?? fetch)(registrationUrl, {
@@ -1068,3 +1096,6 @@ method: 'POST',
     },
-    body: JSON.stringify(clientMetadata),
+    body: JSON.stringify({
+      ...clientMetadata,
+      application_type: applicationType,
+    }),
   });
@@ -1079,2 +1110,18 @@
 
+function inferOAuthApplicationType(redirectUris: string[]): 'native' | 'web' {
+  const isNativeRedirectUri = (redirectUri: string): boolean => {
+    const url = new URL(redirectUri);
+    return (
+      ((url.protocol === 'http:' || url.protocol === 'https:') &&
+        (url.hostname === 'localhost' ||
+          url.hostname.endsWith('.localhost') ||
+          url.hostname === '127.0.0.1' ||
+          url.hostname === '[::1]')) ||
+      (url.protocol !== 'http:' && url.protocol !== 'https:')
+    );
+  };
+
+  return redirectUris.every(isNativeRedirectUri) ? 'native' : 'web';
+}
+
 export async function auth(
@@ -1086,2 +1133,6 @@ provider: OAuthClientProvider,
     callbackState?: string;
+    /**
+     * Value of the `iss` parameter from the authorization response.
+     */
+    callbackIssuer?: string;
     scope?: string;
@@ -1147,2 +1198,3 @@ resourceMetadataUrl?: URL;
     callbackState,
+    callbackIssuer,
     scope,
@@ -1155,2 +1207,3 @@ resourceMetadataUrl,
     callbackState?: string;
+    callbackIssuer?: string;
     scope?: string;
@@ -1212,2 +1265,16 @@ resourceMetadataUrl?: URL;
   let clientInformation = await Promise.resolve(provider.clientInformation());
+  if (clientInformation?.issuer != null) {
+    const storedAuthorizationServerInformation =
+      await getStoredAuthorizationServerInformation({
+        provider,
+        clientInformation,
+      });
+    if (storedAuthorizationServerInformation) {
+      assertAuthorizationServerInformationMatches({
+        storedAuthorizationServerInformation,
+        currentAuthorizationServerInformation,
+      });
+    }
+  }
+
   if (!clientInformation) {
@@ -1261,2 +1328,9 @@ if (authorizationCode !== undefined) {
     }
+    validateAuthorizationResponseIssuer({
+      callbackIssuer,
+      expectedIssuer:
+        storedAuthorizationServerInformation.issuer ??
+        metadata?.issuer ??
+        String(authorizationServerUrl),
+    });
     assertAuthorizationServerInformationMatches({
@@ -1263,0 +1337,0 @@ storedAuthorizationServerInformation,

src/tool/types.ts

@@ -5,5 +5,7 @@ import { z } from 'zod/v4';
 
-export const LATEST_PROTOCOL_VERSION = '2025-11-25';
+export const LATEST_PROTOCOL_VERSION = '2026-07-28';
+export const LATEST_LEGACY_PROTOCOL_VERSION = '2025-11-25';
 export const SUPPORTED_PROTOCOL_VERSIONS = [
   LATEST_PROTOCOL_VERSION,
+  LATEST_LEGACY_PROTOCOL_VERSION,
   '2025-06-18',
@@ -77,3 +79,5 @@ '2025-03-26',
 type BaseParams = z.infer<typeof BaseParamsSchema>;
-export const ResultSchema = BaseParamsSchema;
+export const ResultSchema = BaseParamsSchema.extend({
+  resultType: z.optional(z.string()),
+});
 
@@ -133,2 +137,11 @@ export const RequestSchema = z.object({
 
+export const DiscoverResultSchema = ResultSchema.extend({
+  supportedVersions: z.array(z.string()),
+  capabilities: ServerCapabilitiesSchema,
+  instructions: z.optional(z.string()),
+  ttlMs: z.optional(z.number()),
+  cacheScope: z.optional(z.union([z.literal('public'), z.literal('private')])),
+});
+export type DiscoverResult = z.infer<typeof DiscoverResultSchema>;
+
 export const InitializeResultSchema = ResultSchema.extend({
@@ -160,8 +173,6 @@ protocolVersion: z.string(),
     description: z.optional(z.string()),
-    inputSchema: z
-      .object({
-        type: z.literal('object'),
-        properties: z.optional(z.object({}).loose()),
-      })
-      .loose(),
+    inputSchema: z.looseObject({
+      type: z.optional(z.unknown()),
+      properties: z.optional(z.object({}).loose()),
+    }),
     /**
@@ -168,0 +179,0 @@ * @see https://modelcontextprotocol.io/specification/2025-06-18/server/tools#output-schema

New alerts

URL strings

Supply chain risk

Package contains fragments of external URLs or IP addresses, which the package may be accessing at runtime.

Fixed alerts

AI-detected potential code anomaly

Supply chain risk

AI has identified unusual behaviors that may pose a security risk.

Improved metrics

Total package byte prevSize

653728

11%

Number of package files

32

3.23%

Lines of code

10459

10.4%

Number of lines in readme file

173

9.49%

No dependency changes