diff --git a/.gitignore b/.gitignore
index 6c4bf1a6..b39dd94e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -69,6 +69,9 @@ web_modules/
 # Output of 'npm pack'
 *.tgz
 
+# Output of 'npm run fetch:spec-types'
+src/spec.types.ts
+
 # Yarn Integrity file
 .yarn-integrity
 
diff --git a/package.json b/package.json
index 15b7753b..bbca197b 100644
--- a/package.json
+++ b/package.json
@@ -35,6 +35,7 @@
     "dist"
   ],
   "scripts": {
+    "fetch:spec-types": "test -f src/spec.types.ts || curl -o src/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:esm:w": "npm run build:esm -- -w",
@@ -43,7 +44,7 @@
     "examples:simple-server:w": "tsx --watch src/examples/server/simpleStreamableHttp.ts --oauth",
     "prepack": "npm run build:esm && npm run build:cjs",
     "lint": "eslint src/",
-    "test": "jest",
+    "test": "npm run fetch:spec-types && jest",
     "start": "npm run server",
     "server": "tsx watch --clear-screen=false src/cli.ts server",
     "client": "tsx src/cli.ts client"
diff --git a/src/spec.types.test.ts b/src/spec.types.test.ts
new file mode 100644
index 00000000..b6c88689
--- /dev/null
+++ b/src/spec.types.test.ts
@@ -0,0 +1,657 @@
+// import ts from 'typescript';
+
+import * as SDKTypes from "./types.js";
+import * as SpecTypes from "./spec.types.js";
+
+// Deep version that recursively removes index signatures (caused by ZodObject.passthrough()) and turns unknowns into `object | undefined`
+type DeepKnownKeys<T> = T extends object
+  ? T extends Array<infer U>
+    ? Array<DeepKnownKeys<U>>
+    : T extends Function
+    ? T
+    : {
+        [K in keyof T as string extends K ? never : number extends K ? never : K]: DeepKnownKeys<T[K]>;
+      }
+  : unknown extends T
+  ? (object | undefined)
+  : T;
+
+function checkCancelledNotification(
+  sdk: SDKTypes.CancelledNotification,
+  spec: SpecTypes.CancelledNotification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkBaseMetadata(
+  sdk: SDKTypes.BaseMetadata,
+  spec: DeepKnownKeys<SpecTypes.BaseMetadata>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkImplementation(
+  sdk: SDKTypes.Implementation,
+  spec: DeepKnownKeys<SpecTypes.Implementation>
+) {
+  sdk = spec;
+  spec = sdk;
+} 
+function checkProgressNotification(
+  sdk: SDKTypes.ProgressNotification,
+  spec: DeepKnownKeys<SpecTypes.ProgressNotification>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+
+function checkSubscribeRequest(
+  sdk: SDKTypes.SubscribeRequest,
+  spec: SpecTypes.SubscribeRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkUnsubscribeRequest(
+  sdk: SDKTypes.UnsubscribeRequest,
+  spec: SpecTypes.UnsubscribeRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkPaginatedRequest(
+  sdk: SDKTypes.PaginatedRequest,
+  spec: SpecTypes.PaginatedRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkPaginatedResult(
+  sdk: SDKTypes.PaginatedResult,
+  spec: SpecTypes.PaginatedResult
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListRootsRequest(
+  sdk: SDKTypes.ListRootsRequest,
+  spec: SpecTypes.ListRootsRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListRootsResult(
+  sdk: SDKTypes.ListRootsResult,
+  spec: DeepKnownKeys<SpecTypes.ListRootsResult>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkRoot(sdk: SDKTypes.Root, spec: DeepKnownKeys<SpecTypes.Root>) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkElicitRequest(sdk: SDKTypes.ElicitRequest, spec: DeepKnownKeys<SpecTypes.ElicitRequest>) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkElicitResult(sdk: SDKTypes.ElicitResult, spec: DeepKnownKeys<SpecTypes.ElicitResult>) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkCompleteRequest(sdk: SDKTypes.CompleteRequest, spec: DeepKnownKeys<SpecTypes.CompleteRequest>) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkCompleteResult(sdk: SDKTypes.CompleteResult, spec: SpecTypes.CompleteResult) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkProgressToken(
+  sdk: SDKTypes.ProgressToken,
+  spec: SpecTypes.ProgressToken
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkCursor(sdk: SDKTypes.Cursor, spec: SpecTypes.Cursor) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkRequest(
+  sdk: SDKTypes.Request,
+  spec: SpecTypes.Request
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkResult(
+  sdk: SDKTypes.Result,
+  spec: SpecTypes.Result
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkRequestId(
+  sdk: SDKTypes.RequestId,
+  spec: SpecTypes.RequestId
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkJSONRPCRequest(
+  sdk: SDKTypes.JSONRPCRequest,
+  spec: SpecTypes.JSONRPCRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkJSONRPCNotification(
+  sdk: SDKTypes.JSONRPCNotification,
+  spec: SpecTypes.JSONRPCNotification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkJSONRPCResponse(
+  sdk: SDKTypes.JSONRPCResponse,
+  spec: SpecTypes.JSONRPCResponse
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkEmptyResult(
+  sdk: SDKTypes.EmptyResult,
+  spec: SpecTypes.EmptyResult
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkNotification(
+  sdk: SDKTypes.Notification,
+  spec: SpecTypes.Notification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkClientResult(
+  sdk: SDKTypes.ClientResult,
+  spec: SpecTypes.ClientResult
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkClientNotification(
+  sdk: SDKTypes.ClientNotification,
+  spec: SpecTypes.ClientNotification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkServerResult(
+  sdk: SDKTypes.ServerResult,
+  spec: SpecTypes.ServerResult
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkResourceTemplateReference(
+  sdk: SDKTypes.ResourceTemplateReference,
+  spec: DeepKnownKeys<SpecTypes.ResourceTemplateReference>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkPromptReference(
+  sdk: SDKTypes.PromptReference,
+  spec: DeepKnownKeys<SpecTypes.PromptReference>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkResourceReference(
+  sdk: SDKTypes.ResourceReference,
+  spec: DeepKnownKeys<SpecTypes.ResourceTemplateReference>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkToolAnnotations(
+  sdk: SDKTypes.ToolAnnotations,
+  spec: DeepKnownKeys<SpecTypes.ToolAnnotations>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkTool(
+  sdk: SDKTypes.Tool,
+  spec: DeepKnownKeys<SpecTypes.Tool>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListToolsRequest(
+  sdk: SDKTypes.ListToolsRequest,
+  spec: SpecTypes.ListToolsRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListToolsResult(
+  sdk: SDKTypes.ListToolsResult,
+  spec: DeepKnownKeys<SpecTypes.ListToolsResult>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkCallToolResult(
+  sdk: SDKTypes.CallToolResult,
+  spec: DeepKnownKeys<SpecTypes.CallToolResult>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkCallToolRequest(
+  sdk: SDKTypes.CallToolRequest,
+  spec: SpecTypes.CallToolRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkToolListChangedNotification(
+  sdk: SDKTypes.ToolListChangedNotification,
+  spec: SpecTypes.ToolListChangedNotification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkResourceListChangedNotification(
+  sdk: SDKTypes.ResourceListChangedNotification,
+  spec: SpecTypes.ResourceListChangedNotification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkPromptListChangedNotification(
+  sdk: SDKTypes.PromptListChangedNotification,
+  spec: SpecTypes.PromptListChangedNotification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkRootsListChangedNotification(
+  sdk: SDKTypes.RootsListChangedNotification,
+  spec: SpecTypes.RootsListChangedNotification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkResourceUpdatedNotification(
+  sdk: SDKTypes.ResourceUpdatedNotification,
+  spec: SpecTypes.ResourceUpdatedNotification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkSamplingMessage(
+  sdk: SDKTypes.SamplingMessage,
+  spec: DeepKnownKeys<SpecTypes.SamplingMessage>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkCreateMessageResult(
+  sdk: SDKTypes.CreateMessageResult,
+  spec: DeepKnownKeys<SpecTypes.CreateMessageResult>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkSetLevelRequest(
+  sdk: SDKTypes.SetLevelRequest,
+  spec: SpecTypes.SetLevelRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkPingRequest(
+  sdk: SDKTypes.PingRequest,
+  spec: SpecTypes.PingRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkInitializedNotification(
+  sdk: SDKTypes.InitializedNotification,
+  spec: SpecTypes.InitializedNotification
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListResourcesRequest(
+  sdk: SDKTypes.ListResourcesRequest,
+  spec: SpecTypes.ListResourcesRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListResourcesResult(
+  sdk: SDKTypes.ListResourcesResult,
+  spec: DeepKnownKeys<SpecTypes.ListResourcesResult>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListResourceTemplatesRequest(
+  sdk: SDKTypes.ListResourceTemplatesRequest,
+  spec: SpecTypes.ListResourceTemplatesRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListResourceTemplatesResult(
+  sdk: SDKTypes.ListResourceTemplatesResult,
+  spec: DeepKnownKeys<SpecTypes.ListResourceTemplatesResult>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkReadResourceRequest(
+  sdk: SDKTypes.ReadResourceRequest,
+  spec: SpecTypes.ReadResourceRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkReadResourceResult(
+  sdk: SDKTypes.ReadResourceResult,
+  spec: DeepKnownKeys<SpecTypes.ReadResourceResult>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkResourceContents(
+  sdk: SDKTypes.ResourceContents,
+  spec: DeepKnownKeys<SpecTypes.ResourceContents>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkTextResourceContents(
+  sdk: SDKTypes.TextResourceContents,
+  spec: DeepKnownKeys<SpecTypes.TextResourceContents>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkBlobResourceContents(
+  sdk: SDKTypes.BlobResourceContents,
+  spec: DeepKnownKeys<SpecTypes.BlobResourceContents>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkResource(
+  sdk: SDKTypes.Resource,
+  spec: DeepKnownKeys<SpecTypes.Resource>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkResourceTemplate(
+  sdk: SDKTypes.ResourceTemplate,
+  spec: DeepKnownKeys<SpecTypes.ResourceTemplate>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkPromptArgument(
+  sdk: SDKTypes.PromptArgument,
+  spec: DeepKnownKeys<SpecTypes.PromptArgument>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkPrompt(
+  sdk: SDKTypes.Prompt,
+  spec: DeepKnownKeys<SpecTypes.Prompt>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListPromptsRequest(
+  sdk: SDKTypes.ListPromptsRequest,
+  spec: SpecTypes.ListPromptsRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkListPromptsResult(
+  sdk: SDKTypes.ListPromptsResult,
+  spec: DeepKnownKeys<SpecTypes.ListPromptsResult>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkGetPromptRequest(
+  sdk: SDKTypes.GetPromptRequest,
+  spec: SpecTypes.GetPromptRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkTextContent(
+  sdk: SDKTypes.TextContent,
+  spec: DeepKnownKeys<SpecTypes.TextContent>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkImageContent(
+  sdk: SDKTypes.ImageContent,
+  spec: DeepKnownKeys<SpecTypes.ImageContent>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkAudioContent(
+  sdk: SDKTypes.AudioContent,
+  spec: DeepKnownKeys<SpecTypes.AudioContent>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkEmbeddedResource(
+  sdk: SDKTypes.EmbeddedResource,
+  spec: DeepKnownKeys<SpecTypes.EmbeddedResource>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkResourceLink(
+  sdk: SDKTypes.ResourceLink,
+  spec: DeepKnownKeys<SpecTypes.ResourceLink>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkContentBlock(
+  sdk: SDKTypes.ContentBlock,
+  spec: DeepKnownKeys<SpecTypes.ContentBlock>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkPromptMessage(
+  sdk: SDKTypes.PromptMessage,
+  spec: DeepKnownKeys<SpecTypes.PromptMessage>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkGetPromptResult(
+  sdk: SDKTypes.GetPromptResult,
+  spec: DeepKnownKeys<SpecTypes.GetPromptResult>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkBooleanSchema(
+  sdk: SDKTypes.BooleanSchema,
+  spec: DeepKnownKeys<SpecTypes.BooleanSchema>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkStringSchema(
+  sdk: SDKTypes.StringSchema,
+  spec: DeepKnownKeys<SpecTypes.StringSchema>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkNumberSchema(
+  sdk: SDKTypes.NumberSchema,
+  spec: DeepKnownKeys<SpecTypes.NumberSchema>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkEnumSchema(
+  sdk: SDKTypes.EnumSchema,
+  spec: DeepKnownKeys<SpecTypes.EnumSchema>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkPrimitiveSchemaDefinition(
+  sdk: SDKTypes.PrimitiveSchemaDefinition,
+  spec: DeepKnownKeys<SpecTypes.PrimitiveSchemaDefinition>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkCreateMessageRequest(
+  sdk: DeepKnownKeys<SDKTypes.CreateMessageRequest>, // TODO(quirk): some {} type
+  spec: DeepKnownKeys<SpecTypes.CreateMessageRequest>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkInitializeRequest(
+  sdk: DeepKnownKeys<SDKTypes.InitializeRequest>, // TODO(quirk): some {} type
+  spec: SpecTypes.InitializeRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkInitializeResult(
+  sdk: DeepKnownKeys<SDKTypes.InitializeResult>, // TODO(quirk): some {} type
+  spec: SpecTypes.InitializeResult
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkClientCapabilities(
+  sdk: DeepKnownKeys<SDKTypes.ClientCapabilities>, // TODO(quirk): {}
+  spec: SpecTypes.ClientCapabilities
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkServerCapabilities(
+  sdk: DeepKnownKeys<SDKTypes.ServerCapabilities>, // TODO(quirk): {}
+  spec: SpecTypes.ServerCapabilities
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkJSONRPCError(
+  sdk: DeepKnownKeys<SDKTypes.JSONRPCError>, // TODO(quirk): error.data
+  spec: DeepKnownKeys<SpecTypes.JSONRPCError>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkJSONRPCMessage(
+  sdk: DeepKnownKeys<SDKTypes.JSONRPCMessage>, // TODO(quirk): error.data
+  spec: DeepKnownKeys<SpecTypes.JSONRPCMessage>
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkClientRequest(
+  sdk: DeepKnownKeys<SDKTypes.ClientRequest>, // TODO(quirk): capabilities.logging is {}
+  spec: SpecTypes.ClientRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkServerRequest(
+  sdk: DeepKnownKeys<SDKTypes.ServerRequest>, // TODO(quirk): some {} typ
+  spec: SpecTypes.ServerRequest
+) {
+  sdk = spec;
+  spec = sdk;
+}
+function checkLoggingMessageNotification(
+  sdk: SDKTypes.LoggingMessageNotification,
+  spec: SpecTypes.LoggingMessageNotification
+) {
+  sdk = spec;
+  // spec = sdk; // TODO(bug): data is optional
+}
+function checkServerNotification(
+  sdk: SDKTypes.ServerNotification,
+  spec: SpecTypes.ServerNotification
+) {
+  sdk = spec;
+  // spec = sdk; // TODO(bug): data is optional
+}
+
+// TODO(bug): missing type in SDK
+// function checkModelHint(
+//   sdk: SDKTypes.ModelHint,
+//   spec: DeepKnownKeys<SpecTypes.ModelHint>
+// ) {
+//   sdk = spec;
+//   spec = sdk;
+// }
+
+// TODO(bug): missing type in SDK
+// function checkModelPreferences(
+//   sdk: SDKTypes.ModelPreferences,
+//   spec: DeepKnownKeys<SpecTypes.ModelPreferences>
+// ) {
+//   sdk = spec;
+//   spec = sdk;
+// }
+
+// TODO(bug): missing type in SDK
+// function checkAnnotations(
+//   sdk: SDKTypes.Annotations,
+//   spec: DeepKnownKeys<SpecTypes.Annotations>
+// ) {
+//   sdk = spec;
+//   spec = sdk;
+// }
+
+const SPEC_TYPES_FILE  = 'src/spec.types.ts';
+const THIS_SOURCE_FILE = 'src/spec.types.test.ts';
+
+describe('Spec Types', () => {
+    const specTypesContent = require('fs').readFileSync(SPEC_TYPES_FILE, 'utf-8');
+    const typeNames = [...specTypesContent.matchAll(/export\s+interface\s+(\w+)\b/g)].map(m => m[1]);
+    const testContent = require('fs').readFileSync(THIS_SOURCE_FILE, 'utf-8');
+    
+    it('should define some expected types', () => {
+        expect(typeNames).toContain('JSONRPCNotification');
+        expect(typeNames).toContain('ElicitResult');
+    });
+
+    for (const typeName of typeNames) {
+        it(`${typeName} should have a compatibility test`, () => {
+            expect(testContent).toContain(`function check${typeName}(`);
+        });
+    }
+});
\ No newline at end of file