fix: avoid DOM-only HeadersInit in v1 declarations

.changeset/node-only-normalize-headers.md

@@ -0,0 +1,5 @@
+---
+'@modelcontextprotocol/sdk': patch
+---
+
+Avoid referencing the DOM-only `HeadersInit` global in emitted transport declarations so Node-only TypeScript projects can compile with `skipLibCheck: false`.

src/client/sse.ts

@@ -114,7 +114,7 @@ export class SSEClientTransport implements Transport {
     }
 
     private async _commonHeaders(): Promise<Headers> {
-        const headers: HeadersInit & Record<string, string> = {};
+        const headers: RequestInit['headers'] & Record<string, string> = {};
         if (this._authProvider) {
             const tokens = await this._authProvider.tokens();
             if (tokens) {

src/client/streamableHttp.ts

@@ -181,7 +181,7 @@ export class StreamableHTTPClientTransport implements Transport {
     }
 
     private async _commonHeaders(): Promise<Headers> {
-        const headers: HeadersInit & Record<string, string> = {};
+        const headers: RequestInit['headers'] & Record<string, string> = {};
         if (this._authProvider) {
             const tokens = await this._authProvider.tokens();
             if (tokens) {

src/shared/transport.ts

@@ -3,10 +3,10 @@ import { JSONRPCMessage, MessageExtraInfo, RequestId } from '../types.js';
 export type FetchLike = (url: string | URL, init?: RequestInit) => Promise<Response>;
 
 /**
- * Normalizes HeadersInit to a plain Record<string, string> for manipulation.
+ * Normalizes request headers to a plain Record<string, string> for manipulation.
  * Handles Headers objects, arrays of tuples, and plain objects.
  */
-export function normalizeHeaders(headers: HeadersInit | undefined): Record<string, string> {
+export function normalizeHeaders(headers: RequestInit['headers'] | undefined): Record<string, string> {
     if (!headers) return {};
 
     if (headers instanceof Headers) {