feat: auto-select JSON Schema validator based on runtime (#1456)

packages/client/package.json

@@ -25,6 +25,24 @@
         ".": {
             "types": "./dist/index.d.mts",
             "import": "./dist/index.mjs"
+        },
+        "./_shims": {
+            "workerd": {
+                "types": "./dist/shimsWorkerd.d.mts",
+                "import": "./dist/shimsWorkerd.mjs"
+            },
+            "browser": {
+                "types": "./dist/shimsWorkerd.d.mts",
+                "import": "./dist/shimsWorkerd.mjs"
+            },
+            "node": {
+                "types": "./dist/shimsNode.d.mts",
+                "import": "./dist/shimsNode.mjs"
+            },
+            "default": {
+                "types": "./dist/shimsNode.d.mts",
+                "import": "./dist/shimsNode.mjs"
+            }
         }
     },
     "files": [

packages/client/src/client/client.ts

@@ -1,3 +1,4 @@
+import { DefaultJsonSchemaValidator } from '@modelcontextprotocol/client/_shims';
 import type {
     CallToolRequest,
     ClientCapabilities,
@@ -35,7 +36,6 @@ import type {
     UnsubscribeRequest
 } from '@modelcontextprotocol/core';
 import {
-    AjvJsonSchemaValidator,
     assertClientRequestTaskCapability,
     assertToolsCallTaskCapability,
     CallToolResultSchema,
@@ -153,28 +153,7 @@ export type ClientOptions = ProtocolOptions & {
      * The validator is used to validate structured content returned by tools
      * against their declared output schemas.
      *
-     * @default AjvJsonSchemaValidator
-     *
-     * @example
-     * ```typescript
-     * // ajv
-     * const client = new Client(
-     *   { name: 'my-client', version: '1.0.0' },
-     *   {
-     *     capabilities: {},
-     *     jsonSchemaValidator: new AjvJsonSchemaValidator()
-     *   }
-     * );
-     *
-     * // @cfworker/json-schema
-     * const client = new Client(
-     *   { name: 'my-client', version: '1.0.0' },
-     *   {
-     *     capabilities: {},
-     *     jsonSchemaValidator: new CfWorkerJsonSchemaValidator()
-     *   }
-     * );
-     * ```
+     * @default DefaultJsonSchemaValidator (AjvJsonSchemaValidator on Node.js, CfWorkerJsonSchemaValidator on Cloudflare Workers)
      */
     jsonSchemaValidator?: jsonSchemaValidator;
 
@@ -259,7 +238,7 @@ export class Client<
     ) {
         super(options);
         this._capabilities = options?.capabilities ?? {};
-        this._jsonSchemaValidator = options?.jsonSchemaValidator ?? new AjvJsonSchemaValidator();
+        this._jsonSchemaValidator = options?.jsonSchemaValidator ?? new DefaultJsonSchemaValidator();
         this._enforceStrictCapabilities = options?.enforceStrictCapabilities ?? false;
 
         // Store list changed config for setup after connection (when we know server capabilities)

packages/client/src/shimsNode.ts

@@ -0,0 +1,6 @@
+/**
+ * Node.js runtime shims for client package
+ *
+ * This file is selected via package.json export conditions when running in Node.js.
+ */
+export { AjvJsonSchemaValidator as DefaultJsonSchemaValidator } from '@modelcontextprotocol/core';

packages/client/src/shimsWorkerd.ts

@@ -0,0 +1,6 @@
+/**
+ * Cloudflare Workers runtime shims for client package
+ *
+ * This file is selected via package.json export conditions when running in workerd.
+ */
+export { CfWorkerJsonSchemaValidator as DefaultJsonSchemaValidator } from '@modelcontextprotocol/core';

packages/client/tsconfig.json

@@ -6,7 +6,8 @@
         "paths": {
             "*": ["./*"],
             "@modelcontextprotocol/core": ["./node_modules/@modelcontextprotocol/core/src/index.ts"],
-            "@modelcontextprotocol/test-helpers": ["./node_modules/@modelcontextprotocol/test-helpers/src/index.ts"]
+            "@modelcontextprotocol/test-helpers": ["./node_modules/@modelcontextprotocol/test-helpers/src/index.ts"],
+            "@modelcontextprotocol/client/_shims": ["./src/shimsNode.ts"]
         }
     }
 }

packages/client/tsdown.config.ts

@@ -3,7 +3,7 @@ import { defineConfig } from 'tsdown';
 export default defineConfig({
     // 1. Entry Points
     //    Directly matches package.json include/exclude globs
-    entry: ['src/index.ts'],
+    entry: ['src/index.ts', 'src/shimsNode.ts', 'src/shimsWorkerd.ts'],
 
     // 2. Output Configuration
     format: ['esm'],
@@ -30,5 +30,8 @@ export default defineConfig({
     },
     // 5. Vendoring Strategy - Bundle the code for this specific package into the output,
     //    but treat all other dependencies as external (require/import).
-    noExternal: ['@modelcontextprotocol/core']
+    noExternal: ['@modelcontextprotocol/core'],
+
+    // 6. External packages - keep self-reference imports external for runtime resolution
+    external: ['@modelcontextprotocol/client/_shims']
 });