feat: Automatically use the right validator based on runtime

package.json

@@ -18,6 +18,13 @@
         "modelcontextprotocol",
         "mcp"
     ],
+    "imports": {
+        "#default-validator": {
+            "workerd": "./dist/esm/validation/default-workerd.js",
+            "import": "./dist/esm/validation/default.js",
+            "require": "./dist/cjs/validation/default.js"
+        }
+    },
     "exports": {
         ".": {
             "import": "./dist/esm/index.js",
@@ -60,10 +67,10 @@
     ],
     "scripts": {
         "fetch:spec-types": "curl -o spec.types.ts https://raw.githubusercontent.com/modelcontextprotocol/modelcontextprotocol/refs/heads/main/schema/draft/schema.ts",
-        "build": "npm run build:esm && npm run build:cjs",
-        "build:esm": "mkdir -p dist/esm && echo '{\"type\": \"module\"}' > dist/esm/package.json && tsc -p tsconfig.prod.json",
+        "build": "rm -rf dist && npm run build:esm && npm run build:cjs",
+        "build:esm": "mkdir -p dist/esm && tsc -p tsconfig.prod.json",
         "build:esm:w": "npm run build:esm -- -w",
-        "build:cjs": "mkdir -p dist/cjs && echo '{\"type\": \"commonjs\"}' > dist/cjs/package.json && tsc -p tsconfig.cjs.json",
+        "build:cjs": "mkdir -p dist/cjs && tsc -p tsconfig.cjs.json",
         "build:cjs:w": "npm run build:cjs -- -w",
         "examples:simple-server:w": "tsx --watch src/examples/server/simpleStreamableHttp.ts --oauth",
         "prepack": "npm run build:esm && npm run build:cjs",

src/server/index.ts

@@ -31,7 +31,7 @@ import {
     SetLevelRequestSchema,
     SUPPORTED_PROTOCOL_VERSIONS
 } from '../types.js';
-import { AjvJsonSchemaValidator } from '../validation/ajv-provider.js';
+import DefaultJsonSchemaValidator from '#default-validator';
 import type { JsonSchemaType, jsonSchemaValidator } from '../validation/types.js';
 
 export type ServerOptions = ProtocolOptions & {
@@ -128,7 +128,7 @@ export class Server<
         super(options);
         this._capabilities = options?.capabilities ?? {};
         this._instructions = options?.instructions;
-        this._jsonSchemaValidator = options?.jsonSchemaValidator ?? new AjvJsonSchemaValidator();
+        this._jsonSchemaValidator = options?.jsonSchemaValidator ?? new DefaultJsonSchemaValidator();
 
         this.setRequestHandler(InitializeRequestSchema, request => this._oninitialize(request));
         this.setNotificationHandler(InitializedNotificationSchema, () => this.oninitialized?.());

src/validation/default-workerd.ts

@@ -0,0 +1,3 @@
+import { CfWorkerJsonSchemaValidator } from './cfworker-provider.js';
+
+export default CfWorkerJsonSchemaValidator;

src/validation/default.ts

@@ -0,0 +1,3 @@
+import { AjvJsonSchemaValidator } from './ajv-provider.js';
+
+export default AjvJsonSchemaValidator;

src/validation/index.ts

@@ -2,27 +2,25 @@
  * JSON Schema validation
  *
  * This module provides configurable JSON Schema validation for the MCP SDK.
- * Choose a validator based on your runtime environment:
+ * The SDK automatically selects the appropriate validator based on your runtime
+ * environment using export conditions:
  *
- * - AjvJsonSchemaValidator: Best for Node.js (default, fastest)
- *   Import from: @modelcontextprotocol/sdk/validation/ajv
- *   Requires peer dependencies: ajv, ajv-formats
+ * - Node.js: Automatically uses AjvJsonSchemaValidator (fastest, requires ajv and ajv-formats)
+ * - Cloudflare Workers (workerd): Automatically uses CfWorkerJsonSchemaValidator (requires @cfworker/json-schema)
  *
- * - CfWorkerJsonSchemaValidator: Best for edge runtimes
- *   Import from: @modelcontextprotocol/sdk/validation/cfworker
- *   Requires peer dependency: @cfworker/json-schema
+ * Simply import the default validator and it will work in your environment:
  *
  * @example
  * ```typescript
- * // For Node.js with AJV
- * import { AjvJsonSchemaValidator } from '@modelcontextprotocol/sdk/validation/ajv';
- * const validator = new AjvJsonSchemaValidator();
- *
- * // For Cloudflare Workers
- * import { CfWorkerJsonSchemaValidator } from '@modelcontextprotocol/sdk/validation/cfworker';
- * const validator = new CfWorkerJsonSchemaValidator();
+ * // Automatically selects the right validator for your runtime
+ * import DefaultValidator from '@modelcontextprotocol/sdk/validation/default';
+ * const validator = new DefaultValidator();
  * ```
  *
+ * For advanced use cases, you can also import validators directly:
+ * - `@modelcontextprotocol/sdk/validation/ajv` - AjvJsonSchemaValidator (Node.js)
+ * - `@modelcontextprotocol/sdk/validation/cfworker` - CfWorkerJsonSchemaValidator (edge runtimes)
+ *
  * @module validation
  */
 

tsconfig.json

@@ -14,8 +14,10 @@
         "isolatedModules": true,
         "skipLibCheck": true,
         "baseUrl": ".",
+        "rootDir": "./src",
         "paths": {
-            "pkce-challenge": ["node_modules/pkce-challenge/dist/index.node"]
+            "pkce-challenge": ["node_modules/pkce-challenge/dist/index.node"],
+            "#default-validator": ["./src/validation/default.js"]
         }
     },
     "include": ["src/**/*"],