fix(core): make fromJsonSchema() use runtime-aware default validator … (#1825)

Co-authored-by: Felix Weinberger <3823880+felixweinberger@users.noreply.github.com>

packages/client/src/fromJsonSchema.ts

@@ -0,0 +1,9 @@
+import { DefaultJsonSchemaValidator } from '@modelcontextprotocol/client/_shims';
+import type { JsonSchemaType, jsonSchemaValidator, StandardSchemaWithJSON } from '@modelcontextprotocol/core';
+import { fromJsonSchema as coreFromJsonSchema } from '@modelcontextprotocol/core';
+
+let _defaultValidator: jsonSchemaValidator | undefined;
+
+export function fromJsonSchema<T = unknown>(schema: JsonSchemaType, validator?: jsonSchemaValidator): StandardSchemaWithJSON<T, T> {
+    return coreFromJsonSchema<T>(schema, validator ?? (_defaultValidator ??= new DefaultJsonSchemaValidator()));
+}

packages/client/src/index.ts

@@ -73,5 +73,8 @@ export { StreamableHTTPClientTransport } from './client/streamableHttp.js';
 // experimental exports
 export { ExperimentalClientTasks } from './experimental/tasks/client.js';
 
+// runtime-aware wrapper (shadows core/public's fromJsonSchema with optional validator)
+export { fromJsonSchema } from './fromJsonSchema.js';
+
 // re-export curated public API from core
 export * from '@modelcontextprotocol/core/public';

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

@@ -138,5 +138,6 @@ export type { StandardSchemaWithJSON } from '../../util/standardSchema.js';
 export { AjvJsonSchemaValidator } from '../../validators/ajvProvider.js';
 export type { CfWorkerSchemaDraft } from '../../validators/cfWorkerProvider.js';
 export { CfWorkerJsonSchemaValidator } from '../../validators/cfWorkerProvider.js';
-export { fromJsonSchema } from '../../validators/fromJsonSchema.js';
+// fromJsonSchema is intentionally NOT exported here — the server and client packages
+// provide runtime-aware wrappers that default to the appropriate validator via _shims.
 export type { JsonSchemaType, JsonSchemaValidator, jsonSchemaValidator, JsonSchemaValidatorResult } from '../../validators/types.js';

packages/core/src/validators/fromJsonSchema.ts

@@ -10,6 +10,11 @@ import type { JsonSchemaType, jsonSchemaValidator } from './types.js';
  * The callback arguments will be typed `unknown` (raw JSON Schema has no TypeScript
  * types attached). Cast at the call site, or use the generic `fromJsonSchema<MyType>(...)`.
  *
+ * @param schema - A JSON Schema object describing the expected shape
+ * @param validator - A validator provider. When importing `fromJsonSchema` from
+ *   `@modelcontextprotocol/server` or `@modelcontextprotocol/client`, a runtime-appropriate
+ *   default is provided automatically (AJV on Node.js, CfWorker on edge runtimes).
+ *
  * @example
  * ```ts source="./fromJsonSchema.examples.ts#fromJsonSchema_basicUsage"
  * const inputSchema = fromJsonSchema<{ name: string }>(

packages/server/src/fromJsonSchema.ts

@@ -0,0 +1,9 @@
+import type { JsonSchemaType, jsonSchemaValidator, StandardSchemaWithJSON } from '@modelcontextprotocol/core';
+import { fromJsonSchema as coreFromJsonSchema } from '@modelcontextprotocol/core';
+import { DefaultJsonSchemaValidator } from '@modelcontextprotocol/server/_shims';
+
+let _defaultValidator: jsonSchemaValidator | undefined;
+
+export function fromJsonSchema<T = unknown>(schema: JsonSchemaType, validator?: jsonSchemaValidator): StandardSchemaWithJSON<T, T> {
+    return coreFromJsonSchema<T>(schema, validator ?? (_defaultValidator ??= new DefaultJsonSchemaValidator()));
+}

packages/server/src/index.ts

@@ -43,5 +43,8 @@ export type { CreateTaskRequestHandler, TaskRequestHandler, ToolTaskHandler } fr
 export { ExperimentalMcpServerTasks } from './experimental/tasks/mcpServer.js';
 export { ExperimentalServerTasks } from './experimental/tasks/server.js';
 
+// runtime-aware wrapper (shadows core/public's fromJsonSchema with optional validator)
+export { fromJsonSchema } from './fromJsonSchema.js';
+
 // re-export curated public API from core
 export * from '@modelcontextprotocol/core/public';