feat(core): export type predicates for spec data-model types

Adds isContentBlock, isTool, isImplementation, isResourceLink, and
isEmbeddedResource to the public type-guard surface alongside the existing
isCallToolResult. Each predicate validates against the internal Zod schema.

Lets extension authors validate spec types embedded inside custom-method
payloads (e.g. a CallToolResult inside a ui/notifications/tool-result) without
needing the Zod schemas themselves.

Also moves guards.test.ts from src/types/ to test/types/ so vitest actually
picks it up (the include pattern is test/**/*.test.ts).

Author: felixweinberger

.changeset/spec-type-predicates.md

@@ -0,0 +1,6 @@
+---
+'@modelcontextprotocol/client': patch
+'@modelcontextprotocol/server': patch
+---
+
+Export type predicates (`isContentBlock`, `isTool`, `isImplementation`, `isResourceLink`, `isEmbeddedResource`) for validating spec data-model types embedded in extension payloads. Each predicate performs full structural validation against the spec schema. (`isCallToolResult` was already exported.)

packages/core/src/exports/public/index.ts

@@ -105,14 +105,19 @@ export {
     assertCompleteRequestPrompt,
     assertCompleteRequestResourceTemplate,
     isCallToolResult,
+    isContentBlock,
+    isEmbeddedResource,
+    isImplementation,
     isInitializedNotification,
     isInitializeRequest,
     isJSONRPCErrorResponse,
     isJSONRPCNotification,
     isJSONRPCRequest,
     isJSONRPCResponse,
     isJSONRPCResultResponse,
+    isResourceLink,
     isTaskAugmentedRequestParams,
+    isTool,
     parseJSONRPCMessage
 } from '../../types/guards.js';
 

packages/core/src/types/guards.ts

@@ -1,5 +1,8 @@
 import {
     CallToolResultSchema,
+    ContentBlockSchema,
+    EmbeddedResourceSchema,
+    ImplementationSchema,
     InitializedNotificationSchema,
     InitializeRequestSchema,
     JSONRPCErrorResponseSchema,
@@ -8,13 +11,18 @@ import {
     JSONRPCRequestSchema,
     JSONRPCResponseSchema,
     JSONRPCResultResponseSchema,
-    TaskAugmentedRequestParamsSchema
+    ResourceLinkSchema,
+    TaskAugmentedRequestParamsSchema,
+    ToolSchema
 } from './schemas.js';
 import type {
     CallToolResult,
     CompleteRequest,
     CompleteRequestPrompt,
     CompleteRequestResourceTemplate,
+    ContentBlock,
+    EmbeddedResource,
+    Implementation,
     InitializedNotification,
     InitializeRequest,
     JSONRPCErrorResponse,
@@ -23,7 +31,9 @@ import type {
     JSONRPCRequest,
     JSONRPCResponse,
     JSONRPCResultResponse,
-    TaskAugmentedRequestParams
+    ResourceLink,
+    TaskAugmentedRequestParams,
+    Tool
 } from './types.js';
 
 /**
@@ -81,6 +91,46 @@ export const isCallToolResult = (value: unknown): value is CallToolResult => {
     return CallToolResultSchema.safeParse(value).success;
 };
 
+/**
+ * Checks if a value is a valid {@linkcode ContentBlock}.
+ * @param value - The value to check.
+ *
+ * @returns True if the value is a valid {@linkcode ContentBlock}, false otherwise.
+ */
+export const isContentBlock = (value: unknown): value is ContentBlock => ContentBlockSchema.safeParse(value).success;
+
+/**
+ * Checks if a value is a valid {@linkcode Tool}.
+ * @param value - The value to check.
+ *
+ * @returns True if the value is a valid {@linkcode Tool}, false otherwise.
+ */
+export const isTool = (value: unknown): value is Tool => ToolSchema.safeParse(value).success;
+
+/**
+ * Checks if a value is a valid {@linkcode Implementation}.
+ * @param value - The value to check.
+ *
+ * @returns True if the value is a valid {@linkcode Implementation}, false otherwise.
+ */
+export const isImplementation = (value: unknown): value is Implementation => ImplementationSchema.safeParse(value).success;
+
+/**
+ * Checks if a value is a valid {@linkcode ResourceLink}.
+ * @param value - The value to check.
+ *
+ * @returns True if the value is a valid {@linkcode ResourceLink}, false otherwise.
+ */
+export const isResourceLink = (value: unknown): value is ResourceLink => ResourceLinkSchema.safeParse(value).success;
+
+/**
+ * Checks if a value is a valid {@linkcode EmbeddedResource}.
+ * @param value - The value to check.
+ *
+ * @returns True if the value is a valid {@linkcode EmbeddedResource}, false otherwise.
+ */
+export const isEmbeddedResource = (value: unknown): value is EmbeddedResource => EmbeddedResourceSchema.safeParse(value).success;
+
 /**
  * Checks if a value is a valid {@linkcode TaskAugmentedRequestParams}.
  * @param value - The value to check.

packages/core/src/types/guards.test.ts packages/core/test/types/guards.test.tspackages/core/src/types/guards.test.ts renamed to packages/core/test/types/guards.test.ts

@@ -1,7 +1,17 @@
 import { describe, expect, it } from 'vitest';
 
-import { JSONRPC_VERSION } from './constants.js';
-import { isCallToolResult, isJSONRPCErrorResponse, isJSONRPCResponse, isJSONRPCResultResponse } from './guards.js';
+import { JSONRPC_VERSION } from '../../src/types/constants.js';
+import {
+    isCallToolResult,
+    isContentBlock,
+    isEmbeddedResource,
+    isImplementation,
+    isJSONRPCErrorResponse,
+    isJSONRPCResponse,
+    isJSONRPCResultResponse,
+    isResourceLink,
+    isTool
+} from '../../src/types/guards.js';
 
 describe('isJSONRPCResponse', () => {
     it('returns true for a valid result response', () => {
@@ -121,3 +131,94 @@ describe('isCallToolResult', () => {
         ).toBe(false);
     });
 });
+
+describe('isContentBlock', () => {
+    it('returns true for valid text content', () => {
+        expect(isContentBlock({ type: 'text', text: 'hello' })).toBe(true);
+    });
+
+    it('returns true for valid image content', () => {
+        expect(isContentBlock({ type: 'image', data: 'aGVsbG8=', mimeType: 'image/png' })).toBe(true);
+    });
+
+    it('returns false for invalid type discriminant', () => {
+        expect(isContentBlock({ type: 'invalid', text: 'x' })).toBe(false);
+    });
+
+    it('returns false for non-objects', () => {
+        expect(isContentBlock(null)).toBe(false);
+        expect(isContentBlock(undefined)).toBe(false);
+        expect(isContentBlock('string')).toBe(false);
+    });
+});
+
+describe('isTool', () => {
+    it('returns true for a minimal valid tool', () => {
+        expect(isTool({ name: 'echo', inputSchema: { type: 'object' } })).toBe(true);
+    });
+
+    it('returns false when required fields are missing', () => {
+        expect(isTool({ name: 'echo' })).toBe(false);
+        expect(isTool({ inputSchema: { type: 'object' } })).toBe(false);
+    });
+
+    it('returns false for non-objects', () => {
+        expect(isTool(null)).toBe(false);
+        expect(isTool(undefined)).toBe(false);
+        expect(isTool('string')).toBe(false);
+    });
+});
+
+describe('isImplementation', () => {
+    it('returns true for valid implementation info', () => {
+        expect(isImplementation({ name: 'my-app', version: '1.0.0' })).toBe(true);
+    });
+
+    it('returns false when required fields are missing', () => {
+        expect(isImplementation({ name: 'my-app' })).toBe(false);
+        expect(isImplementation({ version: '1.0.0' })).toBe(false);
+    });
+
+    it('returns false for non-objects', () => {
+        expect(isImplementation(null)).toBe(false);
+        expect(isImplementation(undefined)).toBe(false);
+        expect(isImplementation('string')).toBe(false);
+    });
+});
+
+describe('isResourceLink', () => {
+    it('returns true for a valid resource link', () => {
+        expect(isResourceLink({ type: 'resource_link', uri: 'file:///x', name: 'x' })).toBe(true);
+    });
+
+    it('returns false when required fields are missing', () => {
+        expect(isResourceLink({ type: 'resource_link' })).toBe(false);
+    });
+
+    it('returns false for non-objects', () => {
+        expect(isResourceLink(null)).toBe(false);
+        expect(isResourceLink(undefined)).toBe(false);
+        expect(isResourceLink('string')).toBe(false);
+    });
+});
+
+describe('isEmbeddedResource', () => {
+    it('returns true for a valid embedded resource', () => {
+        expect(
+            isEmbeddedResource({
+                type: 'resource',
+                resource: { uri: 'file:///x', text: 'hello' }
+            })
+        ).toBe(true);
+    });
+
+    it('returns false when resource is missing', () => {
+        expect(isEmbeddedResource({ type: 'resource' })).toBe(false);
+    });
+
+    it('returns false for non-objects', () => {
+        expect(isEmbeddedResource(null)).toBe(false);
+        expect(isEmbeddedResource(undefined)).toBe(false);
+        expect(isEmbeddedResource('string')).toBe(false);
+    });
+});