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docs: correctness and coverage pass for the 2026-07-28 revision (#2389)

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Felix Weinberger 2026-06-29 18:44:25 +01:00 • committed by GitHub
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docs/server.md
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@ -18,12 +18,28 @@ The examples below use these imports. Adjust based on which features and transpo
```ts source="../examples/guides/serverGuide.examples.ts#imports"
import { randomUUID } from 'node:crypto';
import { createServer } from 'node:http';
import { createMcpExpressApp } from '@modelcontextprotocol/express';
import { NodeStreamableHTTPServerTransport } from '@modelcontextprotocol/node';
import type { CallToolResult, ResourceLink } from '@modelcontextprotocol/server';
import { completable, McpServer, ResourceTemplate, TRACEPARENT_META_KEY } from '@modelcontextprotocol/server';
import { StdioServerTransport } from '@modelcontextprotocol/server/stdio';
import type { OAuthTokenVerifier } from '@modelcontextprotocol/express';
import {
createMcpExpressApp,
getOAuthProtectedResourceMetadataUrl,
mcpAuthMetadataRouter,
requireBearerAuth
} from '@modelcontextprotocol/express';
import { NodeStreamableHTTPServerTransport, toNodeHandler } from '@modelcontextprotocol/node';
import type { CallToolResult, InputRequiredResult, OAuthMetadata, ResourceLink } from '@modelcontextprotocol/server';
import {
acceptedContent,
completable,
createMcpHandler,
createRequestStateCodec,
inputRequired,
McpServer,
ResourceTemplate,
TRACEPARENT_META_KEY
} from '@modelcontextprotocol/server';
import { serveStdio, StdioServerTransport } from '@modelcontextprotocol/server/stdio';
import * as z from 'zod/v4';
```
@ -52,6 +68,32 @@ await server.connect(transport);
For a complete server with sessions and the browser-client CORS recipe, see [`legacy-routing/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/legacy-routing/server.ts).
#### Serving the 2026-07-28 draft revision over HTTP
A hand-wired Streamable HTTP transport speaks the 2025-era protocol it was written for. To serve the 2026-07-28 draft revision, use `createMcpHandler`: it builds one instance from your factory per request and, by default, serves 2025-era traffic stateless from the same factory:
```ts source="../examples/guides/serverGuide.examples.ts#createMcpHandler_basic"
const handler = createMcpHandler(() => {
const server = new McpServer({ name: 'my-server', version: '1.0.0' }, { capabilities: { tools: {} } });
// register tools/resources/prompts once; the same factory serves both eras
return server;
});
```
`handler.fetch` is a web-standard `(Request) => Promise<Response>`: on Cloudflare Workers, Deno, or Bun, `export default handler` is all the mounting you need. For Express, Fastify, or plain `node:http`, wrap the handler once with `toNodeHandler` from
`@modelcontextprotocol/node`:
```ts source="../examples/guides/serverGuide.examples.ts#createMcpHandler_node"
createServer(toNodeHandler(handler)).listen(3000);
// Express: app.all('/mcp', toNodeHandler(handler));
// behind express.json(): const node = toNodeHandler(handler); app.all('/mcp', (req, res) => void node(req, res, req.body));
```
**Options:** Pass `legacy: 'reject'` to refuse 2025-era requests with the unsupported-protocol-version error (the default, `'stateless'`, serves them per request with no sessions). `onerror` observes out-of-band errors without altering responses. The entry performs no
Origin/Host validation and no token verification itself. Mount [DNS rebinding protection](#dns-rebinding-protection) in front of it, and pass validated auth through `handler.fetch(request, { authInfo })` (or `req.auth` when using `toNodeHandler`).
To keep an existing sessionful 2025 deployment serving legacy traffic, route with `isLegacyRequest` in front of a strict (`legacy: 'reject'`) handler. See the [2026-07-28 support guide](./migration/support-2026-07-28.md) for the migration patterns; a runnable dual-transport example lives at [`dual-era/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/dual-era/server.ts).
### stdio
For local, process-spawned integrations, use {@linkcode @modelcontextprotocol/server!server/stdio.StdioServerTransport | StdioServerTransport}:
@ -67,20 +109,20 @@ await server.connect(transport);
A hand-constructed stdio server speaks the 2025-era protocol it was written for: nothing about its wire behavior changes when you upgrade the SDK. Serving the 2026-07-28 draft revision goes through the connection-pinned `serveStdio` entry, which mirrors `createMcpHandler` for
long-lived connections — the entry owns the transport and the era decision, and one instance from your factory serves the era the client opened the connection with:
```typescript
import { serveStdio } from '@modelcontextprotocol/server/stdio';
```ts source="../examples/guides/serverGuide.examples.ts#serveStdio_basic"
serveStdio(() => {
const server = new McpServer({ name: 'my-server', version: '1.0.0' }, { capabilities: { tools: {} } });
// register tools/resources/prompts once — the same factory serves both eras
// register tools/resources/prompts once; the same factory serves both eras
return server;
});
```
Plain 2025 clients open with `initialize` and are served exactly as before; 2026-capable clients negotiate via `server/discover` and send each request with the per-request `_meta` envelope, and their connection is pinned to a 2026-era instance. Pass `legacy: 'reject'` to refuse
2025-era openings with the unsupported-protocol-version error. On 2026-pinned connections, read per-request client identity from `ctx.mcpReq.envelope` in your handlers rather than the connection-scoped accessors (see the [2026-07-28 support guide](./migration/support-2026-07-28.md) for details). A runnable
Plain 2025 clients open with `initialize` and are served exactly as before; 2026-capable clients negotiate via `server/discover` and send each request with the per-request `_meta` envelope, and their connection is pinned to a 2026-era instance. On 2026-pinned connections, read per-request client identity from `ctx.mcpReq.envelope` in your handlers rather than the connection-scoped accessors (see the [2026-07-28 support guide](./migration/support-2026-07-28.md) for details). A runnable
example lives at `examples/dual-era/server.ts`, with a two-legged client at `examples/dual-era/client.ts`.
**Options:** `legacy: 'reject'` refuses 2025-era openings with the unsupported-protocol-version error (default `'serve'`). `transport` brings your own `Transport` (for example a `StdioServerTransport` constructed over a socket), and the entry owns it either way. `onerror`
observes out-of-band errors. The returned handle's `close()` tears down the pinned instance and the transport. During era selection the entry may construct and discard a probe instance, so keep factories cheap and side-effect-free.
## Server instructions
Instructions describe how to use the server and its features — cross-tool relationships, workflow patterns, and constraints (see [Instructions](https://modelcontextprotocol.io/specification/latest/basic/lifecycle#instructions) in the MCP specification). Clients may add them to
@ -100,7 +142,8 @@ const server = new McpServer(
Tools let clients invoke actions on your server — they are usually the main way LLMs call into your application (see [Tools](https://modelcontextprotocol.io/docs/learn/server-concepts#tools) in the MCP overview).
Register a tool with {@linkcode @modelcontextprotocol/server!server/mcp.McpServer#registerTool | registerTool}. Provide an `inputSchema` (Zod) to validate arguments, and optionally an `outputSchema` for structured return values.
Register a tool with {@linkcode @modelcontextprotocol/server!server/mcp.McpServer#registerTool | registerTool}. Provide an `inputSchema` (any Standard Schema library that supports JSON Schema conversion: Zod v4 shown here; ArkType and Valibot also conform) to validate
arguments, and optionally an `outputSchema` for structured return values.
> On the 2026-07-28 draft serving path, a tool whose `inputSchema` carries an `x-mcp-header` annotation has that argument mirrored into an `Mcp-Param-{Name}` HTTP request header by conforming clients. `createMcpHandler` validates those headers before dispatch and rejects a
> `tools/call` whose `Mcp-Param-*` headers are missing for a present body value, malformed, or disagree with the body — `400 Bad Request` with JSON-RPC `-32020` (`HeaderMismatch`). `registerTool` warns at registration time when an `x-mcp-header` declaration violates the
@ -299,6 +342,8 @@ server.registerResource(
> **Security note:** If a resource is backed by the filesystem (for example, a `file://` server or a template whose variables map onto file paths), the spec requires sanitizing any user-influenced path before use. Resolve the requested path and verify it stays within
> the intended root directory, rejecting traversal sequences such as `..` (including encoded forms) and symlinks that escape the root. Never pass template variables or client-supplied URIs to filesystem APIs unchecked.
To notify clients when a resource's content changes, see [Change notifications](#change-notifications).
## Prompts
Prompts are reusable templates that help structure interactions with models (see [Prompts](https://modelcontextprotocol.io/docs/learn/server-concepts#prompts) in the MCP overview). Use a prompt when you want to offer a canned interaction pattern that users invoke explicitly; use
@ -358,6 +403,8 @@ server.registerPrompt(
);
```
For resource templates, pass a `complete` callback map to the `ResourceTemplate` constructor instead.
## Extension capabilities
A server advertises support for [MCP extensions](https://modelcontextprotocol.io/specification/latest/basic/lifecycle#capability-negotiation) through `capabilities.extensions` — a map from extension identifier to that extension's settings object. Declare entries with
@ -374,6 +421,44 @@ that extension's settings — `{}` means supported with no settings.
For a runnable pair, see the [`extension-capabilities/` example](../examples/extension-capabilities/README.md); reading the map client-side is covered in the [client guide](./client.md#extension-capabilities).
## Cache hints (2026-07-28 draft)
The 2026-07-28 revision requires `ttlMs` and `cacheScope` on the cacheable results (`tools/list`, `prompts/list`, `resources/list`, `resources/templates/list`, `resources/read`, and `server/discover`) so clients and intermediaries know how long a response stays fresh and
whether it may be shared (SEP-2549). The SDK fills both fields automatically when serving that revision, defaulting to `ttlMs: 0` and `cacheScope: 'private'` (immediately stale, never shared). Responses to 2025-era requests are never affected.
To advertise a real cache policy, set {@linkcode @modelcontextprotocol/server!server/server.ServerOptions | ServerOptions.cacheHints} per operation, and/or `cacheHint` on an individual resource registration:
```ts source="../examples/guides/serverGuide.examples.ts#cacheHints_basic"
const server = new McpServer(
{ name: 'my-server', version: '1.0.0' },
{
cacheHints: {
// The tool list is the same for every caller and rarely changes:
'tools/list': { ttlMs: 60_000, cacheScope: 'public' }
}
}
);
server.registerResource(
'config',
'config://app',
{
mimeType: 'text/plain',
// Wins field-by-field over a cacheHints['resources/read'] entry;
// cacheScope stays at the 'private' default here.
cacheHint: { ttlMs: 300_000 }
},
async uri => ({
contents: [{ uri: uri.href, text: 'App configuration here' }]
})
);
```
Resolution is per field, most specific author first: values set directly on the handler's result, then the resource's `cacheHint`, then the matching `cacheHints` entry, then the defaults.
Invalid hint values throw a `RangeError` at construction/registration time, and the `cacheHint` key is stripped from the resource's listed metadata (it configures the read result, not the listing).
Use `cacheScope: 'public'` only for results that are identical for every caller: a `'public'` result may be served to other users by shared caches. Anything derived from the request's authorization context must stay `'private'` (the default).
## Logging
> [!WARNING]
@ -407,6 +492,9 @@ server.registerTool(
);
```
On a 2026-07-28 request, `ctx.mcpReq.log()` reads its level filter from the request's `io.modelcontextprotocol/logLevel` `_meta` key. When the client did not set one, the call is a silent no-op (the spec forbids sending `notifications/message` without the opt-in). On
2025-era connections the session level set via `logging/setLevel` applies as before. See [2026-07-28 support guide › per-request `logLevel`](./migration/support-2026-07-28.md#ctxmcpreqlog-and-the-per-request-loglevel).
## Progress
Progress notifications let a tool report incremental status updates during long-running operations (see [Progress](https://modelcontextprotocol.io/specification/latest/basic/utilities/progress) in the MCP specification).
@ -446,6 +534,61 @@ server.registerTool(
`progress` must increase on each call. `total` and `message` are optional. If the client does not provide a `progressToken`, skip the notification.
## Change notifications
Servers can signal that their tool, prompt, or resource lists changed, or that a specific resource's content changed, so clients can refresh.
**List changes** are emitted automatically: registering, enabling, disabling, updating, or removing a tool, prompt, or resource sends the matching `notifications/*/list_changed` (`McpServer` advertises the corresponding `listChanged: true` capability on registration;
declare it up front only when using the low-level `Server`). You can also send them explicitly with {@linkcode @modelcontextprotocol/server!server/mcp.McpServer#sendToolListChanged | sendToolListChanged()}, `sendPromptListChanged()`, and `sendResourceListChanged()`.
**Per-resource updates** (2025-era connections) require hand-wiring; `registerResource` has no subscribe option. Declare `resources: { subscribe: true }`, register the `resources/subscribe`/`resources/unsubscribe` handlers on the underlying low-level server, and push
{@linkcode @modelcontextprotocol/server!server/server.Server#sendResourceUpdated | sendResourceUpdated()} when the data changes:
```ts source="../examples/guides/serverGuide.examples.ts#subscriptions_legacy"
const server = new McpServer(
{ name: 'my-server', version: '1.0.0' },
{ capabilities: { resources: { subscribe: true, listChanged: true } } }
);
const subscriptions = new Set<string>();
server.server.setRequestHandler('resources/subscribe', async request => {
subscriptions.add(request.params.uri);
return {};
});
server.server.setRequestHandler('resources/unsubscribe', async request => {
subscriptions.delete(request.params.uri);
return {};
});
// When the underlying data changes:
async function onConfigChanged() {
if (subscriptions.has('config://app')) {
await server.server.sendResourceUpdated({ uri: 'config://app' });
}
}
```
**On the 2026-07-28 revision** clients receive change notifications only on a `subscriptions/listen` stream they open, and the serving entries handle that method themselves (nothing to register). Over HTTP, publish through the handler's typed
{@linkcode @modelcontextprotocol/server!server/serverEventBus.ServerNotifier | notify} facade; each call reaches every open subscription that opted in:
```ts source="../examples/guides/serverGuide.examples.ts#subscriptions_notify"
const handler = createMcpHandler(() => buildServer());
// When the underlying data changes:
handler.notify.resourceUpdated('config://app');
handler.notify.toolsChanged();
```
The default in-process {@linkcode @modelcontextprotocol/server!server/serverEventBus.InMemoryServerEventBus | InMemoryServerEventBus} covers single-process deployments; multi-process deployments supply their own
{@linkcode @modelcontextprotocol/server!server/serverEventBus.ServerEventBus | ServerEventBus} via the `bus` option. On stdio, `serveStdio` pins one instance per connection and routes its ordinary `send*ListChanged()` calls onto open subscriptions automatically. Per-resource updates need one change on a 2026 connection: the subscription bookkeeping lives at the entry (the client's listen filter), so the hand-wired `resources/subscribe` handlers above never run. Publish
`sendResourceUpdated()` unconditionally when the data changes and let the entry deliver it only to subscriptions that listed the URI.
On the 2026-07-28 revision delivery is capability-gated per type: the entry honors `resourceSubscriptions` only when the server advertises `resources: { subscribe: true }`, and each list-changed type only with the matching `listChanged` capability (on 2025-era connections
the SDK gates sends on the presence of the corresponding capability). Clients subscribe to exact resource URIs.
See [`subscriptions/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/subscriptions/server.ts) for a runnable dual-transport example, and the
[2026-07-28 support guide › `subscriptions/listen`](./migration/support-2026-07-28.md#subscriptionslisten) for migration-level detail.
## Trace context propagation
The MCP specification ([SEP-414](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/414)) reserves the unprefixed `_meta` keys `traceparent`, `tracestate`, and `baggage` for distributed trace context, as an exception to the usual `_meta` key prefix rule. When
@ -478,14 +621,128 @@ To propagate context onward (for example on a server-initiated sampling request,
## Server-initiated requests
MCP is bidirectional — servers can send requests _to_ the client during tool execution, as long as the client declares matching capabilities (see [Architecture](https://modelcontextprotocol.io/docs/learn/architecture) in the MCP overview).
MCP is bidirectional: servers can request input _from_ the client during tool execution, as long as the client declares matching capabilities (see [Architecture](https://modelcontextprotocol.io/docs/learn/architecture) in the MCP overview). On 2025-era connections the server pushes a JSON-RPC request to the client (the sections below). On the 2026-07-28 revision there is no server→client request channel: the handler **returns** an `input_required` result carrying the embedded requests,
and the client retries the call with the responses.
On a connection pinned to the 2026-07-28 draft revision (served via `serveStdio` or `createMcpHandler`), the push-style channels below throw an {@linkcode @modelcontextprotocol/server!index.SdkError | SdkError} with
code {@linkcode @modelcontextprotocol/server!index.SdkErrorCode.MethodNotSupportedByProtocolVersion | METHOD_NOT_SUPPORTED_BY_PROTOCOL_VERSION} before anything reaches the wire (see the [2026-07-28 support guide](./migration/support-2026-07-28.md)).
### Requesting input on 2026-07-28: `input_required`
On the 2026-07-28 revision a `tools/call`, `prompts/get`, or `resources/read` handler requests client input by returning {@linkcode @modelcontextprotocol/server!index.inputRequired | inputRequired(...)}. The result names one or more
embedded requests, built with `inputRequired.elicit(...)` (form elicitation), `inputRequired.elicitUrl(...)` (URL elicitation), `inputRequired.createMessage(...)` (sampling), or `inputRequired.listRoots()`. Write the handler **write-once**: on every entry, first read what has already arrived via {@linkcode @modelcontextprotocol/server!index.acceptedContent | acceptedContent(ctx.mcpReq.inputResponses, key)}, and only ask for what is still missing:
```ts source="../examples/guides/serverGuide.examples.ts#registerTool_inputRequired"
server.registerTool(
'deploy',
{
description: 'Deploy after user confirmation',
inputSchema: z.object({ env: z.string() })
},
async ({ env }, ctx): Promise<CallToolResult | InputRequiredResult> => {
const confirmed = acceptedContent<{ confirm: boolean }>(ctx.mcpReq.inputResponses, 'confirm');
if (confirmed?.confirm !== true) {
return inputRequired({
inputRequests: {
confirm: inputRequired.elicit({
message: `Deploy to ${env}?`,
requestedSchema: {
type: 'object',
properties: { confirm: { type: 'boolean' } },
required: ['confirm']
}
})
}
});
}
return { content: [{ type: 'text', text: `Deployed to ${env}` }] };
}
);
```
Every `input_required` result must carry at least one of `inputRequests` or `requestState`: the builder throws a `TypeError` otherwise, and the seam re-checks the rule for hand-built results. Each embedded request is checked against the capabilities the client declared on
the request's `_meta` envelope; a missing capability rejects the call with `-32021` before anything reaches the wire. The responses in `ctx.mcpReq.inputResponses` come from the client; treat them as untrusted input.
On 2025-era connections you don't need to branch: the SDK's legacy shim (on by default) fulfils `input_required` returns by issuing real elicitation/sampling/roots requests over the session, so handlers stay write-once. Knobs and limits are described in [the legacy shim section of the 2026-07-28 support guide](./migration/support-2026-07-28.md#legacy-shim-for-input_required).
For the full multi-step pattern (confirmation, then URL-mode sign-in), see [`mrtr/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/mrtr/server.ts).
#### Carrying state across rounds: `requestState`
The 2026-07-28 serving entries are per-request: nothing survives between rounds on the server. To remember where a multi-step flow stands, return an opaque `requestState` string alongside (or instead of) `inputRequests`; the client echoes it back byte-for-byte on the retry
and the handler reads it back with the typed `ctx.mcpReq.requestState<State>()` accessor.
> [!IMPORTANT]
> `requestState` round-trips through the client and comes back as **attacker-controlled input**. State that influences authorization, resource access, or business logic must be integrity-protected; the SDK applies no protection of its own. Use
> {@linkcode @modelcontextprotocol/server!index.createRequestStateCodec | createRequestStateCodec}, an HMAC-SHA256 codec whose `verify` drops directly into the `ServerOptions.requestState` hook, which runs before the handler and answers tampered or expired state with a
> wire-level `-32602` (frozen message `"Invalid or expired requestState"`). The codec is signed, not encrypted. Do not put secrets in the payload.
```ts source="../examples/guides/serverGuide.examples.ts#requestState_codec"
const stateCodec = createRequestStateCodec<{ step: string }>({
key: crypto.getRandomValues(new Uint8Array(32)), // >= 32 bytes; share across instances in a fleet
ttlSeconds: 600
});
const server = new McpServer(
{ name: 'my-server', version: '1.0.0' },
{ capabilities: { tools: {} }, requestState: { verify: stateCodec.verify } }
);
```
Inside a handler, mint state on the way out and read it back on re-entry. The `requestState.verify` hook has already run by then, and the accessor returns its decoded payload (or the raw string when no hook is configured):
```ts source="../examples/guides/serverGuide.examples.ts#requestState_mintDecode"
server.registerTool(
'wipe-cache',
{ description: 'Confirm, then pick a scope, then wipe', inputSchema: z.object({}) },
async (_args, ctx): Promise<CallToolResult | InputRequiredResult> => {
const state = ctx.mcpReq.requestState<{ step: string }>();
if (state?.step !== 'confirmed') {
const confirmed = acceptedContent<{ confirm: boolean }>(ctx.mcpReq.inputResponses, 'confirm');
if (confirmed?.confirm !== true) {
return inputRequired({
inputRequests: {
confirm: inputRequired.elicit({
message: 'Really wipe the cache?',
requestedSchema: { type: 'object', properties: { confirm: { type: 'boolean' } }, required: ['confirm'] }
})
}
});
}
// Mint only what the response above already proved: the user confirmed.
return inputRequired({
inputRequests: {
scope: inputRequired.elicit({
message: 'Which scope?',
requestedSchema: { type: 'object', properties: { scope: { type: 'string' } }, required: ['scope'] }
})
},
requestState: await stateCodec.mint({ step: 'confirmed' })
});
}
const scope = acceptedContent<{ scope: string }>(ctx.mcpReq.inputResponses, 'scope');
return { content: [{ type: 'text', text: `Wiped ${scope?.scope ?? 'all'}` }] };
}
);
```
Mint state that records what earlier rounds already proved, never an outcome that has not happened yet. The codec makes the token tamper-proof, which means it is bearer proof of whatever you put in it: a token minted as `{ step: 'signed-in' }` before the user signs in grants that step to anyone who echoes it.
See [`mrtr/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/mrtr/server.ts) for the worked end-to-end flow, and the
[2026-07-28 support guide › Replacing per-session state](./migration/support-2026-07-28.md#replacing-per-session-state-requeststate) for porting session-keyed code.
### Sampling
> [!WARNING]
> Sampling is deprecated as of protocol version 2026-07-28 (SEP-2577). It remains fully functional during the deprecation window (at least twelve months); see the [deprecated features registry](https://modelcontextprotocol.io/specification/draft/deprecated). Migrate to
> Sampling is deprecated as of protocol version 2026-07-28 (SEP-2577). It remains fully functional on 2025-era connections during the deprecation window (at least twelve months); see the [deprecated features registry](https://modelcontextprotocol.io/specification/draft/deprecated). Migrate to
> calling LLM provider APIs directly from your server.
> [!NOTE]
> `ctx.mcpReq.requestSampling` is the 2025-era push channel and **throws a typed error on a 2026-07-28-era request**. On that revision, return `inputRequired({ inputRequests: { id: inputRequired.createMessage({ … }) } })` instead; see
> [Requesting input on 2026-07-28](#requesting-input-on-2026-07-28-input_required).
Sampling lets a tool handler request an LLM completion from the connected client — the handler describes a prompt and the client returns the model's response (see [Sampling](https://modelcontextprotocol.io/docs/learn/client-concepts#sampling) in the MCP overview). Use sampling
when a tool needs the model to generate or transform text mid-execution.
@ -535,6 +792,10 @@ Elicitation lets a tool handler request direct input from the user — form fiel
> [!IMPORTANT]
> Sensitive information must not be collected via form elicitation; always use URL elicitation or out-of-band flows for secrets.
> [!NOTE]
> `ctx.mcpReq.elicitInput` is the 2025-era push channel and **throws a typed error on a 2026-07-28-era request**. Return `inputRequired.elicit(...)` (form) or `inputRequired.elicitUrl(...)` (URL) via `inputRequired({ inputRequests: { … } })` instead; see
> [Requesting input on 2026-07-28](#requesting-input-on-2026-07-28-input_required). The throw-style `UrlElicitationRequiredError` (`-32042`) also fails loudly toward 2026-era requests.
Call `ctx.mcpReq.elicitInput(params)` (from {@linkcode @modelcontextprotocol/server!index.ServerContext | ServerContext}) inside a tool handler:
```ts source="../examples/guides/serverGuide.examples.ts#registerTool_elicitation"
@ -583,9 +844,13 @@ For runnable examples, see [`elicitation/server.ts`](https://github.com/modelcon
### Roots
> [!WARNING]
> Roots are deprecated as of protocol version 2026-07-28 (SEP-2577). They remain fully functional during the deprecation window (at least twelve months); see the [deprecated features registry](https://modelcontextprotocol.io/specification/draft/deprecated). Migrate to
> Roots are deprecated as of protocol version 2026-07-28 (SEP-2577). They remain fully functional on 2025-era connections during the deprecation window (at least twelve months); see the [deprecated features registry](https://modelcontextprotocol.io/specification/draft/deprecated). Migrate to
> passing paths via tool parameters, resource URIs, or configuration.
> [!NOTE]
> `server.server.listRoots()` **throws a typed error on a 2026-07-28-era instance**. Return `inputRequired({ inputRequests: { roots: inputRequired.listRoots() } })` and read the response from `ctx.mcpReq.inputResponses` on re-entry; see
> [Requesting input on 2026-07-28](#requesting-input-on-2026-07-28-input_required).
Roots let a tool handler discover the client's workspace directories — for example, to scope a file search or identify project boundaries (see [Roots](https://modelcontextprotocol.io/docs/learn/client-concepts#roots) in the MCP overview). Call {@linkcode
@modelcontextprotocol/server!server/server.Server#listRoots | server.server.listRoots()} (requires the client to declare the `roots` capability):
@ -673,9 +938,53 @@ The app factories also validate the `Origin` header with the same arming rules:
is no option that disables Origin validation for a localhost-class bind. Requests without an `Origin` header always pass, so MCP clients outside a browser are unaffected; a present `Origin` that is not allowed, or that cannot be parsed, is rejected with `403`. The per-framework
middleware (`originValidation`, `localhostOriginValidation`) can also be mounted explicitly, and `@modelcontextprotocol/node` ships equivalent request guards for plain `node:http` servers.
If you use `NodeStreamableHTTPServerTransport` directly with your own HTTP framework, you must implement Host header validation yourself. See the [`hostHeaderValidation`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/packages/middleware/express/src/express.ts)
If you use `NodeStreamableHTTPServerTransport` directly with your own HTTP framework, you must implement Host header validation yourself. See the [`hostHeaderValidation`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/packages/middleware/express/src/middleware/hostHeaderValidation.ts)
middleware source for reference. When mounting a handler bare on a fetch-native runtime, the framework-agnostic helpers from `@modelcontextprotocol/server` (`hostHeaderValidationResponse`, `originValidationResponse`) cover the same checks before the request reaches the handler.
### Authorization (OAuth resource server)
HTTP servers can require OAuth bearer tokens (see [Authorization](https://modelcontextprotocol.io/specification/latest/basic/authorization) in the MCP specification). The SDK treats your server as an OAuth _resource server_: it verifies tokens issued by an authorization
server; it does not issue them. Token verification, the `WWW-Authenticate` challenge, and the [RFC 9728](https://datatracker.ietf.org/doc/html/rfc9728) protected resource metadata document come from `@modelcontextprotocol/express`:
```ts source="../examples/guides/serverGuide.examples.ts#auth_resourceServer"
const mcpServerUrl = new URL('https://api.example.com/mcp');
// Verify tokens however your deployment requires: JWT verification,
// RFC 7662 introspection, a call to your IdP.
const verifier: OAuthTokenVerifier = {
async verifyAccessToken(token) {
const payload = await verifyJwt(token);
return { token, clientId: payload.sub, scopes: payload.scopes, expiresAt: payload.exp };
}
};
// Public deployment: allow-list the public host (see DNS rebinding protection).
const app = createMcpExpressApp({ host: '0.0.0.0', allowedHosts: ['api.example.com'] });
// Serves /.well-known/oauth-protected-resource/mcp (RFC 9728) and mirrors the
// authorization server's metadata, so clients can discover your AS.
app.use(mcpAuthMetadataRouter({ oauthMetadata, resourceServerUrl: mcpServerUrl }));
// 401/403 responses carry `WWW-Authenticate: Bearer …` with `resource_metadata`
// pointing at the document above. That challenge is what starts the client
// SDK's OAuth flow.
const auth = requireBearerAuth({
verifier,
requiredScopes: ['mcp'],
resourceMetadataUrl: getOAuthProtectedResourceMetadataUrl(mcpServerUrl)
});
const node = toNodeHandler(createMcpHandler(buildServer));
app.all('/mcp', auth, (req, res) => void node(req, res, req.body));
```
`requireBearerAuth` attaches the verified `AuthInfo` to `req.auth`; `toNodeHandler` forwards it so tool handlers read it as `ctx.http.authInfo` (and `createMcpHandler` factories as `ctx.authInfo`). A missing or invalid token gets `401 invalid_token`, as does a token whose `expiresAt` is unset or in the past. A valid token missing one of `requiredScopes` gets `403 insufficient_scope`; the challenge's `scope` field is what clients use for scope step-up (SEP-2350).
Authorization Server helpers (`mcpAuthRouter`, `ProxyOAuthServerProvider`, …) live in `@modelcontextprotocol/server-legacy/auth` as a frozen v1 copy; new code should use a dedicated IdP or OAuth library for the AS (see the [FAQ](./faq.md#where-are-the-server-auth-helpers)).
For runnable examples, see [`bearer-auth/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/bearer-auth/server.ts) (minimal static verifier) and
[`oauth/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/oauth/server.ts) (full discovery flow against a demo authorization server).
## See also
- [`examples/`](https://github.com/modelcontextprotocol/typescript-sdk/tree/main/examples) — Full runnable server examples
@ -693,3 +1002,6 @@ middleware source for reference. When mounting a handler bare on a fetch-native
| Resumability | Replay missed SSE events via an event store | [`inMemoryEventStore.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/shared/src/inMemoryEventStore.ts) |
| CORS | Expose MCP headers for browser clients | [`legacy-routing/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/legacy-routing/server.ts) |
| Multi-node deployment | Stateless, persistent-storage, and distributed routing patterns | [`examples/README.md`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/README.md#multi-node-deployment-patterns) |
| Dual-era serving | One factory serving 2025 + 2026-07-28 over HTTP and stdio | [`dual-era/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/dual-era/server.ts) |
| Change notifications | Publish `subscriptions/listen` change events over HTTP and stdio | [`subscriptions/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/subscriptions/server.ts) |
| OAuth resource server | Bearer-token verification, `WWW-Authenticate` challenge, RFC 9728 metadata | [`bearer-auth/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/bearer-auth/server.ts), [`oauth/server.ts`](https://github.com/modelcontextprotocol/typescript-sdk/blob/main/examples/oauth/server.ts) |