feat(client,server): bundle default validators, expose customisation via subpaths (#2088)

packages/client/package.json

@@ -28,6 +28,10 @@
             "types": "./dist/stdio.d.mts",
             "import": "./dist/stdio.mjs"
         },
+        "./validators/ajv": {
+            "types": "./dist/validators/ajv.d.mts",
+            "import": "./dist/validators/ajv.mjs"
+        },
         "./validators/cf-worker": {
             "types": "./dist/validators/cfWorker.d.mts",
             "import": "./dist/validators/cfWorker.mjs"
@@ -54,6 +58,9 @@
     "types": "./dist/index.d.mts",
     "typesVersions": {
         "*": {
+            "validators/ajv": [
+                "dist/validators/ajv.d.mts"
+            ],
             "validators/cf-worker": [
                 "dist/validators/cfWorker.d.mts"
             ],
@@ -93,6 +100,8 @@
         "@modelcontextprotocol/eslint-config": "workspace:^",
         "@modelcontextprotocol/test-helpers": "workspace:^",
         "@cfworker/json-schema": "catalog:runtimeShared",
+        "ajv": "catalog:runtimeShared",
+        "ajv-formats": "catalog:runtimeShared",
         "@types/content-type": "catalog:devTools",
         "@types/cross-spawn": "catalog:devTools",
         "@types/eventsource": "catalog:devTools",

packages/client/src/client/client.ts

@@ -161,7 +161,7 @@ export type ClientOptions = ProtocolOptions & {
      * The validator is used to validate structured content returned by tools
      * against their declared output schemas.
      *
-     * @default {@linkcode DefaultJsonSchemaValidator} ({@linkcode index.AjvJsonSchemaValidator | AjvJsonSchemaValidator} on Node.js, `CfWorkerJsonSchemaValidator` on Cloudflare Workers)
+     * @default Runtime-selected validator (AJV-backed on Node.js, `@cfworker/json-schema`-backed on browser/workerd runtimes)
      */
     jsonSchemaValidator?: jsonSchemaValidator;
 

packages/client/src/shimsNode.ts

@@ -3,7 +3,7 @@
  *
  * This file is selected via package.json export conditions when running in Node.js.
  */
-export { AjvJsonSchemaValidator as DefaultJsonSchemaValidator } from '@modelcontextprotocol/core';
+export { AjvJsonSchemaValidator as DefaultJsonSchemaValidator } from '@modelcontextprotocol/core/validators/ajv';
 
 /**
  * Whether `fetch()` may throw `TypeError` due to CORS. CORS is a browser-only concept —

packages/client/src/validators/ajv.ts

@@ -0,0 +1,14 @@
+/**
+ * Customisation entry point for the AJV validator. Re-exports `Ajv` + `addFormats` from the
+ * SDK's bundled copy, so customising the validator needs no extra installs.
+ *
+ * @example
+ * ```ts
+ * import { Ajv, addFormats, AjvJsonSchemaValidator } from '@modelcontextprotocol/client/validators/ajv';
+ *
+ * const ajv = new Ajv({ strict: true, allErrors: true });
+ * addFormats(ajv);
+ * const validator = new AjvJsonSchemaValidator(ajv);
+ * ```
+ */
+export { addFormats, Ajv, AjvJsonSchemaValidator } from '@modelcontextprotocol/core/validators/ajv';

packages/client/src/validators/cfWorker.ts

@@ -1,10 +1,3 @@
-/**
- * Cloudflare Workers JSON Schema validator, available as a sub-path export.
- *
- * @example
- * ```ts
- * import { CfWorkerJsonSchemaValidator } from '@modelcontextprotocol/client/validators/cf-worker';
- * ```
- */
+/** Customisation entry point for the `@cfworker/json-schema` validator. */
 export type { CfWorkerSchemaDraft } from '@modelcontextprotocol/core/validators/cfWorker';
 export { CfWorkerJsonSchemaValidator } from '@modelcontextprotocol/core/validators/cfWorker';

packages/client/test/client/barrelClean.test.ts

@@ -8,6 +8,8 @@ import { beforeAll, describe, expect, test } from 'vitest';
 const pkgDir = join(dirname(fileURLToPath(import.meta.url)), '../..');
 const distDir = join(pkgDir, 'dist');
 const NODE_ONLY = /\b(child_process|cross-spawn|node:stream|node:child_process)\b/;
+// Anchored at start-of-line so JSDoc-example `from 'ajv'` strings in vendored chunks don't match.
+const VALIDATOR_BACKEND_IMPORT = /^import[^\n]*?from\s+["'](?:ajv|ajv-formats|@cfworker\/json-schema)["']/m;
 
 function chunkImportsOf(entryPath: string): string[] {
     const visited = new Set<string>();
@@ -52,4 +54,17 @@ describe('@modelcontextprotocol/client root entry is browser-safe', () => {
         expect(stdio).toMatch(/\bgetDefaultEnvironment\b/);
         expect(stdio).toMatch(/\bDEFAULT_INHERITED_ENV_VARS\b/);
     });
+
+    test('runtime shims vendor default validator backends instead of requiring consumers to install them', () => {
+        for (const shim of ['shimsNode.mjs', 'shimsWorkerd.mjs', 'shimsBrowser.mjs']) {
+            const entry = join(distDir, shim);
+            expect(readFileSync(entry, 'utf8')).not.toMatch(VALIDATOR_BACKEND_IMPORT);
+
+            for (const chunk of chunkImportsOf(entry)) {
+                expect({ chunk, content: readFileSync(chunk, 'utf8') }).not.toEqual(
+                    expect.objectContaining({ content: expect.stringMatching(VALIDATOR_BACKEND_IMPORT) })
+                );
+            }
+        }
+    });
 });

packages/client/test/client/jsonSchemaValidatorOverride.test.ts

@@ -0,0 +1,110 @@
+import type { JSONRPCMessage, JsonSchemaType, JsonSchemaValidatorResult, jsonSchemaValidator } from '@modelcontextprotocol/core';
+import { InMemoryTransport, LATEST_PROTOCOL_VERSION } from '@modelcontextprotocol/core';
+import { Client } from '../../src/client/client.js';
+import { fromJsonSchema } from '../../src/fromJsonSchema.js';
+
+class RecordingValidator implements jsonSchemaValidator {
+    schemas: JsonSchemaType[] = [];
+    values: unknown[] = [];
+
+    getValidator<T>(schema: JsonSchemaType) {
+        this.schemas.push(schema);
+        return (value: unknown): JsonSchemaValidatorResult<T> => {
+            this.values.push(value);
+            return { valid: true, data: value as T, errorMessage: undefined };
+        };
+    }
+}
+
+async function connectInitializedClient(client: Client) {
+    const [clientTransport, serverTransport] = InMemoryTransport.createLinkedPair();
+    serverTransport.onmessage = async message => {
+        if ('method' in message && 'id' in message && message.method === 'initialize') {
+            await serverTransport.send({
+                jsonrpc: '2.0',
+                id: message.id,
+                result: {
+                    protocolVersion: LATEST_PROTOCOL_VERSION,
+                    capabilities: { tools: {} },
+                    serverInfo: { name: 'test-server', version: '1.0.0' }
+                }
+            });
+        } else if ('method' in message && 'id' in message && message.method === 'tools/list') {
+            await serverTransport.send({
+                jsonrpc: '2.0',
+                id: message.id,
+                result: {
+                    tools: [
+                        {
+                            name: 'structured-tool',
+                            description: 'A tool with structured output',
+                            inputSchema: { type: 'object' },
+                            outputSchema: {
+                                type: 'object',
+                                properties: { count: { type: 'number' } },
+                                required: ['count']
+                            }
+                        }
+                    ]
+                }
+            } satisfies JSONRPCMessage);
+        }
+    };
+
+    await Promise.all([client.connect(clientTransport), serverTransport.start()]);
+    return { clientTransport, serverTransport };
+}
+
+describe('client JSON Schema validator overrides', () => {
+    test('Client constructor uses a custom validator for tool output schema caching', async () => {
+        const validator = new RecordingValidator();
+        const client = new Client(
+            { name: 'test-client', version: '1.0.0' },
+            {
+                capabilities: {},
+                jsonSchemaValidator: validator
+            }
+        );
+        const { clientTransport, serverTransport } = await connectInitializedClient(client);
+
+        await expect(client.listTools()).resolves.toMatchObject({
+            tools: [
+                {
+                    name: 'structured-tool',
+                    outputSchema: {
+                        type: 'object',
+                        properties: { count: { type: 'number' } },
+                        required: ['count']
+                    }
+                }
+            ]
+        });
+
+        expect(validator.schemas).toEqual([
+            {
+                type: 'object',
+                properties: { count: { type: 'number' } },
+                required: ['count']
+            }
+        ]);
+
+        await client.close();
+        await clientTransport.close();
+        await serverTransport.close();
+    });
+
+    test('fromJsonSchema uses an explicitly supplied custom validator', async () => {
+        const validator = new RecordingValidator();
+        const schema: JsonSchemaType = {
+            type: 'object',
+            properties: { name: { type: 'string' } },
+            required: ['name']
+        };
+
+        const standardSchema = fromJsonSchema<{ name: string }>(schema, validator);
+        expect(standardSchema['~standard'].validate({ name: 123 })).toEqual({ value: { name: 123 } });
+
+        expect(validator.schemas).toEqual([schema]);
+        expect(validator.values).toEqual([{ name: 123 }]);
+    });
+});

packages/client/tsconfig.json

@@ -7,6 +7,7 @@
             "*": ["./*"],
             "@modelcontextprotocol/core": ["./node_modules/@modelcontextprotocol/core/src/index.ts"],
             "@modelcontextprotocol/core/public": ["./node_modules/@modelcontextprotocol/core/src/exports/public/index.ts"],
+            "@modelcontextprotocol/core/validators/ajv": ["./node_modules/@modelcontextprotocol/core/src/validators/ajvProvider.ts"],
             "@modelcontextprotocol/core/validators/cfWorker": [
                 "./node_modules/@modelcontextprotocol/core/src/validators/cfWorkerProvider.ts"
             ],

packages/client/tsdown.config.ts

@@ -2,39 +2,35 @@ import { defineConfig } from 'tsdown';
 
 export default defineConfig({
     failOnWarn: 'ci-only',
-    // 1. Entry Points
-    //    Directly matches package.json include/exclude globs
-    entry: ['src/index.ts', 'src/stdio.ts', 'src/shimsNode.ts', 'src/shimsWorkerd.ts', 'src/shimsBrowser.ts', 'src/validators/cfWorker.ts'],
-
-    // 2. Output Configuration
+    entry: [
+        'src/index.ts',
+        'src/stdio.ts',
+        'src/shimsNode.ts',
+        'src/shimsWorkerd.ts',
+        'src/shimsBrowser.ts',
+        'src/validators/ajv.ts',
+        'src/validators/cfWorker.ts'
+    ],
     format: ['esm'],
     outDir: 'dist',
-    clean: true, // Recommended: Cleans 'dist' before building
+    clean: true,
     sourcemap: true,
-
-    // 3. Platform & Target
     target: 'esnext',
     platform: 'node',
-    shims: true, // Polyfills common Node.js shims (__dirname, etc.)
-
-    // 4. Type Definitions
-    //    Bundles d.ts files into a single output
+    shims: true,
     dts: {
         resolver: 'tsc',
-        // override just for DTS generation:
+        resolve: ['ajv', 'ajv-formats'],
         compilerOptions: {
             baseUrl: '.',
             paths: {
                 '@modelcontextprotocol/core': ['../core/src/index.ts'],
                 '@modelcontextprotocol/core/public': ['../core/src/exports/public/index.ts'],
+                '@modelcontextprotocol/core/validators/ajv': ['../core/src/validators/ajvProvider.ts'],
                 '@modelcontextprotocol/core/validators/cfWorker': ['../core/src/validators/cfWorkerProvider.ts']
             }
         }
     },
-    // 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'],
-
-    // 6. External packages - keep self-reference imports external for runtime resolution
+    noExternal: ['@modelcontextprotocol/core', 'ajv', 'ajv-formats', '@cfworker/json-schema'],
     external: ['@modelcontextprotocol/client/_shims']
 });