modelcontextprotocol/typescript-sdk @modelcontextprotocol/server@2.0.0

on GitHub

Minor Changes

• #2501 1480241 Thanks @felixweinberger! - Export the Protocol base class and mergeCapabilities from the @modelcontextprotocol/client and @modelcontextprotocol/server package roots, restoring the v1 import for consumers that subclass Protocol (e.g. the MCP Apps SDK). The client and server packages each bundle their own compiled copy of the class, so import it from one package consistently within a process.

  The codemod now rewrites Protocol and mergeCapabilities imports from shared/protocol.js to the client or server package root, like the module's other symbols, instead of dropping them with an action-required marker.

• #2477 8e1d2e9 Thanks @felixweinberger! - Move the schema source modules (spec schemas, OAuth schemas, protocol constants) into @modelcontextprotocol/core and resolve them from there as a regular runtime dependency instead of bundling a private copy into each package. An application importing more than one of the packages now evaluates a single shared schema graph with shared object identity. @modelcontextprotocol/core gains a ./internal subpath (SDK-internal contract; may change in any release) and the four packages now version together.

• #2513 f413763 Thanks @felixweinberger! - Align the 2026-07-28 wire with the final revision (spec PR #3002): serverInfo moves from the DiscoverResult body to the result _meta, and the per-request envelope's clientInfo demotes from required to SHOULD.

  Before this change the SDK shipped the pre-#3002 shape in both directions: the client hard-rejected a conforming server's DiscoverResult (missing body serverInfo failed parse, so the probe misclassified the server as legacy and attempted an initialize handshake against it — a hard connect failure against a modern-only server such as go-sdk v1.7.0-pre.3), and the server rejected conforming clients that omit clientInfo.

  Now:

  • The 2026 wire schemas are the final revision exactly: no body serverInfo on DiscoverResult, envelope clientInfo optional (a present-but-malformed value still fails validation).
  • Servers stamp _meta['io.modelcontextprotocol/serverInfo'] on every 2026-era response (spec SHOULD; a handler-authored value wins, the 2025-era wire is untouched). This includes the entry-built subscriptions/listen graceful-close results — the spec's SubscriptionsListenResultMeta extends ResultMetaObject.
  • Clients keep sending clientInfo and read server identity from the discover result's _meta only. A server that stamps no identity is anonymous: getServerVersion() is undefined and the response cache partitions under a per-connection surrogate. A malformed _meta serverInfo value is treated as absent on receive (the spec marks the field self-reported, unverified, and display-only).
  • Breaking type changes: DiscoverResult no longer declares serverInfo; RequestMetaEnvelope's clientInfo is optional. New public constant SERVER_INFO_META_KEY ('io.modelcontextprotocol/serverInfo').

• #2369 24be404 Thanks @mattzcarey! - Allow inputRequired.elicit() to accept a Standard Schema such as a Zod object for requestedSchema. The builder converts it to MCP's restricted form-elicitation JSON Schema, while the same schema can validate and type the response through acceptedContent() on handler re-entry. Zod formats mapping to email, uri, date, and date-time are supported. Shapes the restricted schema cannot express reject before anything is sent — nested objects, .regex() and customized zod format patterns, exclusive number bounds (.positive()/.gt()), literal unions (use z.enum or z.literal(['a', 'b'])), and non-spec root keywords like z.strictObject()'s additionalProperties.

• #2541 470678d Thanks @mattzcarey! - Add configurable SSE keep-alive comment frames to Streamable HTTP transports and apply createMcpHandler's existing keepAliveMs option to every HTTP SSE stream it serves.

• #2420 7635115 Thanks @felixweinberger! - Add runtime-neutral Bearer authentication to @modelcontextprotocol/server:
  requireBearerAuth gates web-standard fetch(request) hosts (Cloudflare
  Workers, Deno, Bun, Hono), built on the exported verifyBearerToken and
  bearerAuthChallengeResponse pieces, with OAuthTokenVerifier now defined
  here. The Express middleware adapts the same core and is unchanged in
  behavior, except that WWW-Authenticate challenge values are now RFC 7235
  quoted-string sanitized (quotes and backslashes escaped, control and
  non-ASCII characters replaced); @modelcontextprotocol/express re-exports
  OAuthTokenVerifier as before.

• #2422 61866d7 Thanks @felixweinberger! - Add runtime-neutral OAuth discovery serving to @modelcontextprotocol/server:
  oauthMetadataResponse serves the RFC 9728 Protected Resource Metadata and
  RFC 8414 Authorization Server metadata documents from web-standard
  fetch(request) hosts, built on the exported
  buildOAuthProtectedResourceMetadata, with
  getOAuthProtectedResourceMetadataUrl now defined here. The Express metadata
  router adapts the same core and is unchanged in behavior; the insecure-issuer
  escape hatch is an explicit dangerouslyAllowInsecureIssuerUrl option in the
  neutral core instead of a module-scope environment read. The web-standard
  matcher validates lazily so unmatched traffic always falls through, tolerates
  a trailing slash, supports HEAD, and marks reflected CORS preflights with
  Vary.

• #2483 3f07a32 Thanks @felixweinberger! - Add preloadSchemas(), an explicit opt-in to eager wire-schema construction, and call it automatically in the Cloudflare Workers builds. The wire schemas are built lazily by default, which is the right trade on process-per-invocation runtimes — but on isolate platforms that bill request CPU while module evaluation runs during isolate warm-up, laziness moves construction into the first request each fresh isolate serves. Calling preloadSchemas() at module scope (it is synchronous and idempotent) moves that one-time cost back to module evaluation; the packages' workerd export condition now does this automatically, while the Node and browser builds stay lazy. The server package gains a dedicated browser shim for this (its browser condition previously reused the workerd shim), so browser bundles keep lazy construction.

Patch Changes

• #2402 a400259 Thanks @felixweinberger! - First beta release of SDK v2 with support for the MCP 2026-07-28 specification
  revision. See the migration guides for upgrading from v1
  (docs/migration/upgrade-to-v2.md) and adopting the 2026-07-28 revision
  (docs/migration/support-2026-07-28.md).

• #2456 44797d7 Thanks @felixweinberger! - Restore the v1 parse tolerance for CallToolResult.content: an inbound legacy-era tools/call result without content defaults to [] instead of failing validation. Deployed servers — accepted by SDK v1 for years — return structuredContent-only (or otherwise content-less) results, and the strict parse turned every such call into an INVALID_RESULT error before application code could run.

  The silent-empty-success hazard the strictness guarded is preserved where it matters: the 2025 era's wire-seam schema refuses to default content for a body carrying another result family's vocabulary (task, inputRequests, requestState — the era is frozen, so the list is complete), and the 2026-era wire schemas stay strict — modern-revision servers have no legacy excuse. Task interop through an explicit result schema is untouched (including bodies that also stamp a foreign resultType), and the server-side authoring normalization refuses the same foreign-family vocabulary.

  Server-side authoring is era-independent: a handler result without content (dynamic/JS callers — the TypeScript surface requires it) is normalized to content: [] before era validation on every leg, reaching the wire spec-valid.

  Conscious call: the nested sampling ToolResultContentSchema stays spec-strict — v1 had defaulted its content too, but it is params-side (tool results a caller authors into a sampling message), deliberately not restored.

• #2431 1b90c96 Thanks @morluto! - Fix the CommonJS validators/ajv subpath so reading the exported Ajv class no longer throws ReferenceError: import_ajv is not defined. The subpath now re-exports the bundled provider's concrete Ajv value in CJS output, matching the existing ESM behavior.

• #2405 f172626 Thanks @mattzcarey! - Ship CommonJS builds alongside ESM. Each package now emits both .mjs/.d.mts
  and .cjs/.d.cts (via tsdown format: ['esm', 'cjs']), and its exports map
  adds a require condition so require('@modelcontextprotocol/…') works from
  CommonJS consumers. Output extensions are normalized across all packages
  (@modelcontextprotocol/core moves from .js/.d.ts to .mjs/.d.mts); the
  public import paths are unchanged.

• #2441 561c6d8 Thanks @felixweinberger! - POSTs whose Content-Type media type is not application/json are now
  rejected with 415 Unsupported Media Type; the header is parsed instead of
  substring-matched. Previously any value merely containing the substring
  passed the check (for example text/plain; a=application/json), case
  variants were wrongly rejected, and the 2026-07-28 entry did not inspect
  Content-Type at all — requests with a missing or non-JSON header that used
  to be served on that path now also answer 415. Values with parameters
  (application/json; charset=utf-8, including malformed parameter sections
  like application/json;) continue to work. SDK clients always send the
  correct header and are unaffected.

  The new isJsonContentType(header) helper is exported for transport and
  framework-adapter authors — custom entries composing the exported building
  blocks (classifyInboundRequest, PerRequestHTTPServerTransport) must apply
  it themselves. The hono adapter's JSON body pre-parse and the client's
  response dispatch now use the same parsed-media-type comparison.

• #2384 ce2f65d Thanks @felixweinberger! - instanceof on the SDK error classes (ProtocolError and its typed subclasses, SdkError/SdkHttpError, OAuthError, and the client's SseError, UnauthorizedError, and OAuth-client-flow error family — OAuthClientFlowError and its subclasses) now works across separately bundled copies of the SDK. The classes match by a stable brand (via Symbol.hasInstance and a registry symbol) instead of prototype identity, so a process that uses both @modelcontextprotocol/client and @modelcontextprotocol/server - a gateway, host, or in-process test - can check errors constructed by either package against the class re-exported by the other. Ordinary prototype-based instanceof is preserved as a fallback; user-defined subclasses keep plain prototype semantics. Notes: cross-bundle matching requires both copies to be at or after this release; brands assert identity, not field shape, across versions - keep reading fields defensively. As a side effect, a foreign-bundle SdkError used as an abort reason is now rethrown as-is instead of being wrapped as a RequestTimeout. Branded hierarchies additionally expose an explicit static guard, X.isInstance(value), that reads the same brand and narrows in TypeScript — an alternative for codebases that prefer predicate-style checks over instanceof. Also: UnauthorizedError now sets error.name to 'UnauthorizedError' (previously 'Error'), and per-package conformance tests enforce that every exported error class participates in branding. Version-negotiation probing now recognizes UnauthorizedError (previously a dead name-string check) and propagates it unchanged, so connect() on an auth-gated server rejects with the original UnauthorizedError (previously wrapped as the cause of an SdkError(EraNegotiationFailed)) — run finishAuth() and reconnect, and the retry probes with the token.

• #2458 7c49b47 Thanks @felixweinberger! - Construct the default Ajv validation engine lazily on first validation. Creating a Client or Server no longer pays the ajv + ajv-formats instantiation cost at startup when no JSON Schema validation ever runs.

• #2476 e0a0ab7 Thanks @felixweinberger! - Build protocol-revision wire schemas lazily on first validation instead of at import. Each revision's schema set is now constructed by a module-level memoized factory, so importing the client or server package no longer pays the construction cost of both frozen wire-schema graphs up front. Method membership in the revision registries stays static, the schemas themselves are unchanged, and registry lookups keep returning reference-identical schema objects.

• #2451 7e69735 Thanks @mattzcarey! - Return JSON-RPC Invalid Params with the original URI and an invalid_uri reason when resources/read receives a syntactically malformed URI.

• #2399 3c7ddaf Thanks @felixweinberger! - Return HTTP 400 for a MissingRequiredClientCapabilityError (-32021) produced after dispatch. The spec mandates 400 Bad Request for this error with no condition on where it arose, but only the pre-dispatch capability gate honored that; the post-handler emission — the input_required gate rejecting an embedded request whose required capability the caller did not declare — surfaced in-band on HTTP 200. The JSON-RPC error body is unchanged, every other error code (including a handler relaying a downstream peer's -32020/-32022) keeps the origin-keyed in-band behavior, and the mapping only applies while the response is uncommitted: an exchange that already streamed — or one hosted with responseMode: 'sse', which opens its stream at dispatch end — keeps its committed 200 and carries the error in-stream.

• #2425 e8de519 Thanks @Sehlani042! - Stop advertising validator provider classes from the root client/server type declarations. The provider classes remain available from the explicit validator subpaths.

• #2453 0ab5d14 Thanks @mattzcarey! - Strip RFC 9110 optional whitespace around inbound MCP-Protocol-Version, Mcp-Method, and Mcp-Name values before classifying and validating modern HTTP requests. This keeps valid requests portable across Fetch runtimes that expose raw leading or trailing SP/HTAB through Headers.get().

• #2534 f130e1a Thanks @felixweinberger! - The default validator now honors declared 2019-09 and draft-07/06 dialects instead of rejecting them: a schema stamped "$schema": "http://json-schema.org/draft-07/schema#" (zod-to-json-schema's default output) validates with draft-07 semantics, and a 2019-09 stamp (zod-to-json-schema's 2019-09/openAi targets) with 2019-09 semantics, on both the Ajv and Cloudflare Workers providers (with known engine differences documented in the migration guide). Schemas with no $schema still validate as 2020-12, and unknown dialects still produce the typed error (now listing the supported dialects: 2020-12, 2019-09, draft-07, draft-06).

• Updated dependencies [a400259, 44797d7, f172626, 8e1d2e9, f413763]:

  • @modelcontextprotocol/core@2.0.0