Align SEP-2575 checks with spec PR #3002: serverInfo in result _meta, clientInfo optional (#403)

Spec PR #3002 (part of the final 2026-07-28 revision) moved serverInfo from
the DiscoverResult body to _meta['io.modelcontextprotocol/serverInfo'] and
demoted the request envelope's clientInfo from required to SHOULD. The
checks still asserted the old shape, failing SDKs that follow the final
revision.

- Vendor schema types at spec commit 71e30695.
- server-stateless: drop the missing-clientInfo rejection case and assert
  the opposite (a clientInfo-less request must be served, new check
  sep-2575-request-meta-client-info-optional); discover no longer requires
  body serverInfo; new SHOULD-level check
  sep-2575-server-identifies-in-result-meta (WARNING when the _meta
  identity is absent, SKIPPED when discover itself failed).
- request-metadata (client side): the clientInfo SHOULD moves out of the
  MUST check into its own id sep-2575-client-sends-client-info (WARNING on
  absence), so requirement levels never blend in one check id.
- Mock servers and the everything-server example emit the _meta identity
  and accept clientInfo-less requests.

Author: felixweinberger

examples/servers/typescript/everything-server.ts

@@ -1266,11 +1266,11 @@ app.post('/mcp', async (req, res) => {
 
     // Per-Request Metadata Integrity Checks (Fields verification).
     // A request missing any required `_meta` field is malformed: -32602 and,
-    // on HTTP, status 400 Bad Request.
+    // on HTTP, status 400 Bad Request. `clientInfo` is a SHOULD since spec
+    // PR #3002 and is never required.
     if (
       !meta ||
       !meta['io.modelcontextprotocol/protocolVersion'] ||
-      !meta['io.modelcontextprotocol/clientInfo'] ||
       !meta['io.modelcontextprotocol/clientCapabilities']
     ) {
       return res.status(400).json({
@@ -1372,7 +1372,13 @@ app.post('/mcp', async (req, res) => {
             // served on this path, so the capability must be declared too.
             resources: {}
           },
-          serverInfo: { name: 'everything-stateless-server', version: '1.0.0' }
+          // Spec PR #3002: server identity lives in the result `_meta`.
+          _meta: {
+            'io.modelcontextprotocol/serverInfo': {
+              name: 'everything-stateless-server',
+              version: '1.0.0'
+            }
+          }
         }
       });
     }

src/mock-server/mock-server.test.ts

@@ -252,7 +252,10 @@ describe('createServerStateless', () => {
       );
       expect(status).toBe(200);
       expect(body.result.supportedVersions).toEqual(STATELESS_SPEC_VERSIONS);
-      expect(body.result.serverInfo.name).toBe('conformance-mock-server');
+      // Spec PR #3002: server identity lives in the result `_meta`.
+      expect(body.result._meta['io.modelcontextprotocol/serverInfo'].name).toBe(
+        'conformance-mock-server'
+      );
     } finally {
       await srv.close();
     }

src/mock-server/stateless.ts

@@ -1,8 +1,9 @@
 /**
  * Stateless mock server: 2026-x lifecycle (SEP-2575).
  *
- * No initialize handshake. Validates `_meta` (protocolVersion / clientInfo /
- * clientCapabilities) and the `MCP-Protocol-Version` header on every request,
+ * No initialize handshake. Validates `_meta` (protocolVersion /
+ * clientCapabilities — `clientInfo` is a SHOULD since spec PR #3002 and is
+ * never required) and the `MCP-Protocol-Version` header on every request,
  * serves `server/discover`, and routes other methods to the supplied handlers.
  * Implemented with raw express so it can front-run SDK support.
  */
@@ -14,9 +15,13 @@ import type { MockServer, RequestHandlers } from './index';
 import { STATELESS_SPEC_VERSIONS } from '../connection/select';
 import { capabilitiesFromHandlers } from './stateful';
 
+/**
+ * The required per-request `_meta` keys. `io.modelcontextprotocol/clientInfo`
+ * is deliberately absent: spec PR #3002 demoted it to SHOULD, so a request
+ * without it is valid.
+ */
 const META_KEYS = [
   'io.modelcontextprotocol/protocolVersion',
-  'io.modelcontextprotocol/clientInfo',
   'io.modelcontextprotocol/clientCapabilities'
 ] as const;
 
@@ -156,7 +161,14 @@ export function validateStatelessRequest(
         result: withRequiredDraftResultFields(method, {
           supportedVersions,
           capabilities,
-          serverInfo: { name: 'conformance-mock-server', version: '1.0.0' }
+          // Spec PR #3002: server identity lives in the result `_meta`, not
+          // the DiscoverResult body.
+          _meta: {
+            'io.modelcontextprotocol/serverInfo': {
+              name: 'conformance-mock-server',
+              version: '1.0.0'
+            }
+          }
         })
       }
     };

src/scenarios/client/request-metadata.ts

@@ -32,6 +32,7 @@ const STATUS_SEVERITY: Record<CheckStatus, number> = {
 export const DECLARED_CHECK_IDS = [
   'sep-2575-http-client-sends-version-header',
   'sep-2575-client-populates-meta',
+  'sep-2575-client-sends-client-info',
   'sep-2575-http-version-header-matches-meta',
   'sep-2575-client-declares-roots-capability',
   'sep-2575-client-declares-sampling-capability',
@@ -161,17 +162,19 @@ export class RequestMetadataScenario implements Scenario {
 
       // 2. "Every client request MUST include the following
       //  io.modelcontextprotocol/* fields in _meta: protocolVersion,
-      //  clientInfo, clientCapabilities."
+      //  clientCapabilities." clientInfo is a SHOULD since spec PR #3002 and
+      // is tracked by its own check below, so requirement levels never blend
+      // in one check id.
       const hasClientInfo = meta?.['io.modelcontextprotocol/clientInfo'];
       const hasCapabilities =
         meta?.['io.modelcontextprotocol/clientCapabilities'];
-      const metaIsValid = metaVersion && hasClientInfo && hasCapabilities;
+      const metaIsValid = metaVersion && hasCapabilities;
 
       this.addOrUpdateCheck({
         id: 'sep-2575-client-populates-meta',
         name: 'ClientPopulatesMeta',
         description:
-          'Client populates _meta on every request with all three required fields',
+          'Client populates _meta on every request with the required fields (protocolVersion, clientCapabilities)',
         status: metaIsValid ? 'SUCCESS' : 'FAILURE',
         timestamp: new Date().toISOString(),
         specReferences: [
@@ -183,6 +186,24 @@ export class RequestMetadataScenario implements Scenario {
         details: { method: request.method, meta }
       });
 
+      // 2b. clientInfo SHOULD (spec PR #3002): absence is a WARNING, never a
+      // FAILURE — a dedicated id so adoption is trackable on its own.
+      this.addOrUpdateCheck({
+        id: 'sep-2575-client-sends-client-info',
+        name: 'ClientSendsClientInfo',
+        description:
+          "Client SHOULD include io.modelcontextprotocol/clientInfo in every request's _meta (spec PR #3002)",
+        status: hasClientInfo ? 'SUCCESS' : 'WARNING',
+        timestamp: new Date().toISOString(),
+        specReferences: [
+          {
+            id: 'SEP-2575',
+            url: 'https://modelcontextprotocol.io/specification/draft/basic/index#meta'
+          }
+        ],
+        details: { method: request.method, meta }
+      });
+
       // 3. "The header value MUST match the io.modelcontextprotocol/protocolVersion
       //  field carried in the request body's _meta." Only comparable when both
       // are present; absence is already covered by the two checks above, so

src/scenarios/server/stateless.ts

@@ -29,13 +29,14 @@ export class ServerStatelessScenario implements ClientScenario {
 **Server Implementation Requirements:**
 
 **Endpoints**:
-- \`server/discover\`: Returns supportedVersions, capabilities, and serverInfo metadata.
+- \`server/discover\`: Returns supportedVersions and capabilities; SHOULD identify itself via \`_meta['io.modelcontextprotocol/serverInfo']\` (spec PR #3002).
 - \`tools/call\`: Implement structural test tools like \`test_missing_capability\` requiring explicit capabilities in \`_meta\`.
 
 **Grouped Specification Requirements**:
 
-1. **Per-Request _meta Validation (5 Checks)**
-   - Rejects requests missing \`_meta\` or lacking structural required internal subfields (\`protocolVersion\`, \`clientInfo\`, \`clientCapabilities\`) with a JSON-RPC \`-32602 Invalid params\` error signature and an HTTP status code \`400 Bad Request\`.
+1. **Per-Request _meta Validation (4 Checks)**
+   - Rejects requests missing \`_meta\` or lacking structural required internal subfields (\`protocolVersion\`, \`clientCapabilities\`) with a JSON-RPC \`-32602 Invalid params\` error signature and an HTTP status code \`400 Bad Request\`.
+   - Serves requests whose \`_meta\` omits \`clientInfo\` (a SHOULD since spec PR #3002 — servers MUST NOT require it).
 2. **Discovery & Capabilities (3 Checks)**
    - Implements \`server/discover\` mapping exact mandatory protocol elements.
    - Dynamically checks prompt capability declaration constraints, validates that active RPC handlers match advertised discovery capacities.
@@ -332,20 +333,8 @@ export class ServerStatelessScenario implements ClientScenario {
         },
         rpcId: 102
       },
-      {
-        slug: 'missing-client-info',
-        description:
-          'Rejects request with _meta missing io.modelcontextprotocol/clientInfo',
-        params: {
-          _meta: {
-            'io.modelcontextprotocol/protocolVersion':
-              validMeta['io.modelcontextprotocol/protocolVersion'],
-            'io.modelcontextprotocol/clientCapabilities':
-              validMeta['io.modelcontextprotocol/clientCapabilities']
-          }
-        },
-        rpcId: 103
-      },
+      // No 'missing-client-info' case: spec PR #3002 demoted clientInfo to
+      // SHOULD, so its absence is valid (asserted positively below).
       {
         slug: 'missing-client-capabilities',
         description:
@@ -411,6 +400,45 @@ export class ServerStatelessScenario implements ClientScenario {
       );
     }
 
+    // Positive companion (spec PR #3002): clientInfo is a SHOULD — a request
+    // whose _meta omits it MUST be served, not rejected.
+    const noClientInfoProbe = await sendRpc(
+      'server/discover',
+      {
+        _meta: {
+          'io.modelcontextprotocol/protocolVersion':
+            validMeta['io.modelcontextprotocol/protocolVersion'],
+          'io.modelcontextprotocol/clientCapabilities':
+            validMeta['io.modelcontextprotocol/clientCapabilities']
+        }
+      },
+      undefined,
+      105
+    ).catch(() => null);
+    const noClientInfoData: any = noClientInfoProbe?.data;
+    await runCheck(
+      'sep-2575-request-meta-client-info-optional',
+      'RequestMetaClientInfoOptional',
+      'Serves requests whose _meta omits io.modelcontextprotocol/clientInfo (clientInfo is a SHOULD).',
+      () => {
+        if (!noClientInfoProbe)
+          return { error: 'clientInfo-less probe failed completely' };
+        if (noClientInfoData?.error) {
+          return {
+            error: `Expected a result, got error ${noClientInfoData.error.code}: ${noClientInfoData.error.message}`,
+            details: { response: noClientInfoData }
+          };
+        }
+        if (noClientInfoProbe.res?.status !== 200) {
+          return {
+            error: `Expected HTTP 200, got status code ${noClientInfoProbe.res?.status}`,
+            details: { response: noClientInfoData }
+          };
+        }
+        return { details: { response: noClientInfoData } };
+      }
+    );
+
     // ==========================================
     // 2. Discovery & Capabilities (4 Checks)
     // ==========================================
@@ -448,10 +476,12 @@ export class ServerStatelessScenario implements ClientScenario {
       () => {
         if (discoverRpcError)
           return { error: `Discovery failed: ${discoverRpcError.message}` };
+        // Mandatory body fields per the final revision (spec PR #3002 removed
+        // body serverInfo — identity is a SHOULD in the result _meta, checked
+        // separately below).
         if (
           !discoverResult?.supportedVersions ||
-          !discoverResult?.capabilities ||
-          !discoverResult?.serverInfo
+          !discoverResult?.capabilities
         ) {
           return {
             error: 'Missing mandatory fields in discover response setup',
@@ -462,6 +492,38 @@ export class ServerStatelessScenario implements ClientScenario {
       }
     );
 
+    await runCheck(
+      'sep-2575-server-identifies-in-result-meta',
+      'ServerIdentifiesInResultMeta',
+      "Servers SHOULD identify themselves via _meta['io.modelcontextprotocol/serverInfo'] on responses (spec PR #3002).",
+      () => {
+        if (discoverRpcError)
+          // Discover itself failed (already a FAILURE on the implements-
+          // discover check): nothing is known about identity, so the gap
+          // must not read as an intentional absence.
+          return {
+            skipped: true,
+            details: {
+              note: `Prerequisite missing: ${discoverRpcError.message}`
+            }
+          };
+        const metaServerInfo =
+          discoverResult?._meta?.['io.modelcontextprotocol/serverInfo'];
+        if (!metaServerInfo?.name || !metaServerInfo?.version) {
+          const bodyServerInfo = discoverResult?.serverInfo;
+          return {
+            // SHOULD-level: WARNING, never FAILURE.
+            warning: true,
+            error: bodyServerInfo
+              ? 'serverInfo found only in the pre-#3002 result body, not in _meta'
+              : 'No serverInfo in the discover result _meta',
+            details: { result: discoverResult }
+          };
+        }
+        return { details: { serverInfo: metaServerInfo } };
+      }
+    );
+
     await runCheck(
       'sep-2575-server-declares-prompts-in-discover',
       'ServerDeclaresPromptsInDiscover',

src/spec-types/2025-03-26.ts

@@ -1234,9 +1234,7 @@ export type ClientResult = EmptyResult | CreateMessageResult | ListRootsResult;
 
 /* Server messages */
 export type ServerRequest =
-  | PingRequest
-  | CreateMessageRequest
-  | ListRootsRequest;
+  PingRequest | CreateMessageRequest | ListRootsRequest;
 
 export type ServerNotification =
   | CancelledNotification

src/spec-types/2025-06-18.ts

@@ -6,10 +6,7 @@
  * @category JSON-RPC
  */
 export type JSONRPCMessage =
-  | JSONRPCRequest
-  | JSONRPCNotification
-  | JSONRPCResponse
-  | JSONRPCError;
+  JSONRPCRequest | JSONRPCNotification | JSONRPCResponse | JSONRPCError;
 
 /** @internal */
 export const LATEST_PROTOCOL_VERSION = "2025-06-18";
@@ -1134,11 +1131,7 @@ export interface Annotations {
  * @category Content
  */
 export type ContentBlock =
-  | TextContent
-  | ImageContent
-  | AudioContent
-  | ResourceLink
-  | EmbeddedResource;
+  TextContent | ImageContent | AudioContent | ResourceLink | EmbeddedResource;
 
 /**
  * Text provided to or from an LLM.
@@ -1490,10 +1483,7 @@ export interface ElicitRequest extends Request {
  * @category `elicitation/create`
  */
 export type PrimitiveSchemaDefinition =
-  | StringSchema
-  | NumberSchema
-  | BooleanSchema
-  | EnumSchema;
+  StringSchema | NumberSchema | BooleanSchema | EnumSchema;
 
 /**
  * @category `elicitation/create`
@@ -1586,18 +1576,12 @@ export type ClientNotification =
 
 /** @internal */
 export type ClientResult =
-  | EmptyResult
-  | CreateMessageResult
-  | ListRootsResult
-  | ElicitResult;
+  EmptyResult | CreateMessageResult | ListRootsResult | ElicitResult;
 
 /* Server messages */
 /** @internal */
 export type ServerRequest =
-  | PingRequest
-  | CreateMessageRequest
-  | ListRootsRequest
-  | ElicitRequest;
+  PingRequest | CreateMessageRequest | ListRootsRequest | ElicitRequest;
 
 /** @internal */
 export type ServerNotification =