feat(server): accept Standard Schemas for elicitation

.changeset/standard-schema-elicitation.md

@@ -0,0 +1,8 @@
+---
+'@modelcontextprotocol/core-internal': minor
+'@modelcontextprotocol/server': minor
+'@modelcontextprotocol/client': minor
+---
+
+Allow form elicitation requests to accept Standard Schema values such as Zod objects for `requestedSchema`. The server converts these schemas to MCP's restricted elicitation JSON Schema before sending and parses accepted content with the original schema before returning typed
+results. Zod string formats that map to MCP's supported `email`, `uri`, `date`, or `date-time` formats are accepted; arbitrary regex patterns remain rejected because form elicitation does not carry JSON Schema `pattern`.

docs/migration.md

@@ -693,10 +693,18 @@ server.setRequestHandler('tools/call', async (request, ctx) => {
         requestedSchema: { type: 'object', properties: { name: { type: 'string' } } }
     });
 
+    // Or pass a Standard Schema such as a Zod object for typed content.
+    const typedElicitResult = await ctx.mcpReq.elicitInput({
+        message: 'Please provide details',
+        requestedSchema: z.object({ name: z.string().meta({ title: 'Name' }) })
+    });
+
     return { content: [{ type: 'text', text: 'done' }] };
 });
 ```
 
+Standard Schemas passed to `elicitInput` are converted to MCP's restricted form-elicitation JSON Schema before being sent. They must describe a flat object with primitive properties; accepted responses are parsed with the original schema before `result.content` is returned. With Zod v4, use `.meta({ title: 'Field Label' })` for short form-field labels. Zod string helpers that emit the supported `email`, `uri`, `date`, or `date-time` formats are accepted; arbitrary `.regex()` patterns are rejected because form elicitation does not carry JSON Schema `pattern`.
+
 These replace the pattern of calling `server.sendLoggingMessage()`, `server.createMessage()`, and `server.elicitInput()` from within handlers.
 
 ### Error hierarchy refactoring

docs/server.md

@@ -497,6 +497,11 @@ 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.
 
+For form elicitation, pass either the restricted JSON Schema shape used by the MCP wire protocol or a Standard Schema such as a Zod object. Standard Schemas are converted to the restricted elicitation JSON Schema before being sent, so they must describe a flat object with
+primitive properties (`string`, `number`, `integer`, `boolean`, or string enum fields). When the user accepts the form, `result.content` is parsed with the original Standard Schema and is typed as that schema's output. With Zod v4, use `.meta({ title: 'Field Label' })` for short
+form-field labels; `.describe()` maps to JSON Schema `description`, not `title`. Zod string helpers that emit the supported `email`, `uri`, `date`, or `date-time` formats are accepted; arbitrary `.regex()` patterns are rejected because form elicitation does not carry JSON Schema
+`pattern`.
+
 Call `ctx.mcpReq.elicitInput(params)` (from {@linkcode @modelcontextprotocol/server!index.ServerContext | ServerContext}) inside a tool handler:
 
 ```ts source="../examples/server/src/serverGuide.examples.ts#registerTool_elicitation"
@@ -510,19 +515,10 @@ server.registerTool(
         const result = await ctx.mcpReq.elicitInput({
             mode: 'form',
             message: 'Please share your feedback:',
-            requestedSchema: {
-                type: 'object',
-                properties: {
-                    rating: {
-                        type: 'number',
-                        title: 'Rating (1\u20135)',
-                        minimum: 1,
-                        maximum: 5
-                    },
-                    comment: { type: 'string', title: 'Comment' }
-                },
-                required: ['rating']
-            }
+            requestedSchema: z.object({
+                rating: z.number().min(1).max(5).meta({ title: 'Rating (1-5)' }),
+                comment: z.string().optional().meta({ title: 'Comment' })
+            })
         });
         if (result.action === 'accept') {
             return {

examples/server/src/elicitationFormExample.ts

@@ -13,6 +13,7 @@ import { createMcpExpressApp } from '@modelcontextprotocol/express';
 import { NodeStreamableHTTPServerTransport } from '@modelcontextprotocol/node';
 import { isInitializeRequest, McpServer } from '@modelcontextprotocol/server';
 import type { Request, Response } from 'express';
+import * as z from 'zod/v4';
 
 // Create a fresh MCP server per client connection to avoid shared state between clients.
 // The validator supports format validation (email, date, etc.) if ajv-formats is installed.
@@ -38,51 +39,23 @@ const getServer = () => {
         },
         async () => {
             try {
+                const registrationSchema = z.object({
+                    username: z.string().min(3).max(20).meta({ title: 'Username', description: 'Your desired username (3-20 characters)' }),
+                    email: z.email().meta({ title: 'Email', description: 'Your email address' }),
+                    password: z.string().min(8).meta({ title: 'Password', description: 'Your password (min 8 characters)' }),
+                    newsletter: z.boolean().default(false).meta({ title: 'Newsletter', description: 'Subscribe to newsletter?' })
+                });
+
                 // Request user information through form elicitation
                 const result = await mcpServer.server.elicitInput({
                     mode: 'form',
                     message: 'Please provide your registration information:',
-                    requestedSchema: {
-                        type: 'object',
-                        properties: {
-                            username: {
-                                type: 'string',
-                                title: 'Username',
-                                description: 'Your desired username (3-20 characters)',
-                                minLength: 3,
-                                maxLength: 20
-                            },
-                            email: {
-                                type: 'string',
-                                title: 'Email',
-                                description: 'Your email address',
-                                format: 'email'
-                            },
-                            password: {
-                                type: 'string',
-                                title: 'Password',
-                                description: 'Your password (min 8 characters)',
-                                minLength: 8
-                            },
-                            newsletter: {
-                                type: 'boolean',
-                                title: 'Newsletter',
-                                description: 'Subscribe to newsletter?',
-                                default: false
-                            }
-                        },
-                        required: ['username', 'email', 'password']
-                    }
+                    requestedSchema: registrationSchema
                 });
 
                 // Handle the different possible actions
                 if (result.action === 'accept' && result.content) {
-                    const { username, email, newsletter } = result.content as {
-                        username: string;
-                        email: string;
-                        password: string;
-                        newsletter?: boolean;
-                    };
+                    const { username, email, newsletter } = result.content;
 
                     return {
                         content: [

examples/server/src/serverGuide.examples.ts

@@ -418,19 +418,10 @@ function registerTool_elicitation(server: McpServer) {
             const result = await ctx.mcpReq.elicitInput({
                 mode: 'form',
                 message: 'Please share your feedback:',
-                requestedSchema: {
-                    type: 'object',
-                    properties: {
-                        rating: {
-                            type: 'number',
-                            title: 'Rating (1\u20135)',
-                            minimum: 1,
-                            maximum: 5
-                        },
-                        comment: { type: 'string', title: 'Comment' }
-                    },
-                    required: ['rating']
-                }
+                requestedSchema: z.object({
+                    rating: z.number().min(1).max(5).meta({ title: 'Rating (1-5)' }),
+                    comment: z.string().optional().meta({ title: 'Comment' })
+                })
             });
             if (result.action === 'accept') {
                 return {

packages/codemod/src/generated/versions.ts

@@ -1,9 +1,9 @@
 // AUTO-GENERATED — do not edit. Run `pnpm run generate:versions` to regenerate.
 export const V2_PACKAGE_VERSIONS: Record<string, string> = {
-    '@modelcontextprotocol/client': '^2.0.0-alpha.2',
-    '@modelcontextprotocol/server': '^2.0.0-alpha.2',
-    '@modelcontextprotocol/node': '^2.0.0-alpha.2',
-    '@modelcontextprotocol/express': '^2.0.0-alpha.2',
-    '@modelcontextprotocol/server-legacy': '^2.0.0-alpha.2',
-    '@modelcontextprotocol/core': '^2.0.0-alpha.0'
+    '@modelcontextprotocol/client': '^2.0.0-alpha.3',
+    '@modelcontextprotocol/server': '^2.0.0-alpha.3',
+    '@modelcontextprotocol/node': '^2.0.0-alpha.3',
+    '@modelcontextprotocol/express': '^2.0.0-alpha.3',
+    '@modelcontextprotocol/server-legacy': '^2.0.0-alpha.3',
+    '@modelcontextprotocol/core': '^2.0.0-alpha.1'
 };

packages/core-internal/src/exports/public/index.ts

@@ -44,6 +44,8 @@ export { getDisplayName } from '../../shared/metadataUtils';
 export type {
     BaseContext,
     ClientContext,
+    ElicitInputFormParams,
+    ElicitInputResult,
     NotificationOptions,
     ProgressCallback,
     ProtocolOptions,

packages/core-internal/src/shared/protocol.ts

@@ -42,7 +42,7 @@ import {
     ProtocolErrorCode,
     SUPPORTED_PROTOCOL_VERSIONS
 } from '../types/index';
-import type { StandardSchemaV1 } from '../util/standardSchema';
+import type { StandardSchemaV1, StandardSchemaWithJSON } from '../util/standardSchema';
 import { isStandardSchema, validateStandardSchema } from '../util/standardSchema';
 import type { Transport, TransportSendOptions } from './transport';
 
@@ -203,6 +203,18 @@ export type BaseContext = {
     };
 };
 
+export type ElicitInputFormParams<Schema extends StandardSchemaWithJSON = StandardSchemaWithJSON> = Omit<
+    ElicitRequestFormParams,
+    'requestedSchema'
+> & {
+    requestedSchema: Schema;
+};
+
+export type ElicitInputResult<Schema extends StandardSchemaWithJSON> = Result & {
+    action: ElicitResult['action'];
+    content?: StandardSchemaWithJSON.InferOutput<Schema>;
+};
+
 /**
  * Context provided to server-side request handlers, extending {@linkcode BaseContext} with server-specific fields.
  */
@@ -221,7 +233,13 @@ export type ServerContext = BaseContext & {
         /**
          * Send an elicitation request to the client, requesting user input.
          */
-        elicitInput: (params: ElicitRequestFormParams | ElicitRequestURLParams, options?: RequestOptions) => Promise<ElicitResult>;
+        elicitInput: {
+            <Schema extends StandardSchemaWithJSON>(
+                params: ElicitInputFormParams<Schema>,
+                options?: RequestOptions
+            ): Promise<ElicitInputResult<Schema>>;
+            (params: ElicitRequestFormParams | ElicitRequestURLParams, options?: RequestOptions): Promise<ElicitResult>;
+        };
 
         /**
          * Request LLM sampling from the client.

packages/server/src/server/elicitation.ts

@@ -0,0 +1,142 @@
+import type { ElicitInputFormParams, ElicitRequestFormParams, StandardSchemaWithJSON } from '@modelcontextprotocol/core-internal';
+import {
+    ElicitRequestFormParamsSchema,
+    parseSchema,
+    ProtocolError,
+    ProtocolErrorCode,
+    standardSchemaToJsonSchema
+} from '@modelcontextprotocol/core-internal';
+
+export type NormalizedElicitInputFormParams = {
+    params: ElicitRequestFormParams;
+    standardSchema?: StandardSchemaWithJSON;
+};
+
+function isJsonObject(value: unknown): value is Record<string, unknown> {
+    return typeof value === 'object' && value !== null && !Array.isArray(value);
+}
+
+const ZOD_ISO_DATE_PATTERN = String.raw`(?:(?:\d\d[2468][048]|\d\d[13579][26]|\d\d0[48]|[02468][048]00|[13579][26]00)-02-29|\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\d|30)|(?:02)-(?:0[1-9]|1\d|2[0-8])))`;
+const ZOD_ISO_TIME_PREFIX = String.raw`(?:[01]\d|2[0-3]):[0-5]\d`;
+const ZOD_ISO_OFFSET_PATTERN = String.raw`([+-](?:[01]\d|2[0-3]):[0-5]\d)`;
+
+const ZOD_REDUNDANT_FORMAT_PATTERNS: ReadonlyMap<string, ReadonlySet<string>> = new Map([
+    ['email', new Set([String.raw`^(?!\.)(?!.*\.\.)([A-Za-z0-9_'+\-\.]*)[A-Za-z0-9_+-]@([A-Za-z0-9][A-Za-z0-9\-]*\.)+[A-Za-z]{2,}$`])],
+    [
+        'date',
+        new Set([
+            String.raw`^(?:(?:\d\d[2468][048]|\d\d[13579][26]|\d\d0[48]|[02468][048]00|[13579][26]00)-02-29|\d{4}-(?:(?:0[13578]|1[02])-(?:0[1-9]|[12]\d|3[01])|(?:0[469]|11)-(?:0[1-9]|[12]\d|30)|(?:02)-(?:0[1-9]|1\d|2[0-8])))$`
+        ])
+    ]
+]);
+
+const ZOD_DATETIME_ZONE_SUFFIXES = [
+    String.raw`(?:Z)`,
+    String.raw`(?:Z|)`,
+    String.raw`(?:Z|${ZOD_ISO_OFFSET_PATTERN})`,
+    String.raw`(?:Z||${ZOD_ISO_OFFSET_PATTERN})`
+] as const;
+
+function escapeRegExpLiteral(value: string): string {
+    return value.replaceAll(/[.*+?^${}()|[\]\\]/g, match => `\\${match}`);
+}
+
+const ZOD_PRECISION_TIME_PATTERN = new RegExp(String.raw`^${escapeRegExpLiteral(String.raw`${ZOD_ISO_TIME_PREFIX}:[0-5]\d\.\d{`)}\d+\}$`);
+
+function isZodIsoDatetimePattern(pattern: string): boolean {
+    const prefix = `^${ZOD_ISO_DATE_PATTERN}T(?:`;
+    if (!pattern.startsWith(prefix) || !pattern.endsWith(')$')) {
+        return false;
+    }
+
+    const innerPattern = pattern.slice(prefix.length, -2);
+    const zoneSuffix = ZOD_DATETIME_ZONE_SUFFIXES.find(suffix => innerPattern.endsWith(suffix));
+    if (!zoneSuffix) {
+        return false;
+    }
+
+    const timePattern = innerPattern.slice(0, -zoneSuffix.length);
+    return (
+        timePattern === String.raw`${ZOD_ISO_TIME_PREFIX}` ||
+        timePattern === String.raw`${ZOD_ISO_TIME_PREFIX}:[0-5]\d` ||
+        timePattern === String.raw`${ZOD_ISO_TIME_PREFIX}(?::[0-5]\d(?:\.\d+)?)?` ||
+        ZOD_PRECISION_TIME_PATTERN.test(timePattern)
+    );
+}
+
+function isRedundantFormatPattern(original: Record<string, unknown>, parsed: Record<string, unknown>, key: string): boolean {
+    if (
+        key !== 'pattern' ||
+        typeof original.pattern !== 'string' ||
+        parsed.type !== 'string' ||
+        typeof parsed.format !== 'string' ||
+        original.format !== parsed.format
+    ) {
+        return false;
+    }
+
+    if (parsed.format === 'date-time') {
+        return isZodIsoDatetimePattern(original.pattern);
+    }
+
+    return ZOD_REDUNDANT_FORMAT_PATTERNS.get(parsed.format)?.has(original.pattern) === true;
+}
+
+function findStrippedJsonSchemaPaths(original: unknown, parsed: unknown, path = ''): string[] {
+    if (Array.isArray(original) && Array.isArray(parsed)) {
+        return original.flatMap((item, index) => findStrippedJsonSchemaPaths(item, parsed[index], `${path}[${index}]`));
+    }
+
+    if (!isJsonObject(original) || !isJsonObject(parsed)) {
+        return [];
+    }
+
+    return Object.entries(original).flatMap(([key, value]) => {
+        const childPath = path ? `${path}.${key}` : key;
+        if (!Object.prototype.hasOwnProperty.call(parsed, key)) {
+            if (isRedundantFormatPattern(original, parsed, key)) {
+                return [];
+            }
+            return [childPath];
+        }
+        return findStrippedJsonSchemaPaths(value, parsed[key], childPath);
+    });
+}
+
+function isElicitInputSchema(
+    schema: ElicitRequestFormParams['requestedSchema'] | StandardSchemaWithJSON
+): schema is StandardSchemaWithJSON {
+    return typeof schema === 'object' && schema !== null && '~standard' in schema;
+}
+
+export function normalizeElicitInputFormParams(
+    params: ElicitRequestFormParams | ElicitInputFormParams<StandardSchemaWithJSON>
+): NormalizedElicitInputFormParams {
+    const formParams =
+        params.mode === 'form' ? (params as ElicitRequestFormParams) : { ...(params as ElicitRequestFormParams), mode: 'form' as const };
+
+    if (isElicitInputSchema(formParams.requestedSchema)) {
+        const standardSchema = formParams.requestedSchema;
+        const normalizedParams = {
+            ...formParams,
+            requestedSchema: standardSchemaToJsonSchema(standardSchema, 'input')
+        };
+        const parsedParams = parseSchema(ElicitRequestFormParamsSchema, normalizedParams);
+        if (!parsedParams.success) {
+            throw new ProtocolError(
+                ProtocolErrorCode.InvalidParams,
+                `Elicitation requestedSchema only supports flat primitive properties (string, number, integer, boolean, and string enums): ${parsedParams.error.message}`
+            );
+        }
+        const strippedSchemaPaths = findStrippedJsonSchemaPaths(normalizedParams.requestedSchema, parsedParams.data.requestedSchema);
+        if (strippedSchemaPaths.length > 0) {
+            throw new ProtocolError(
+                ProtocolErrorCode.InvalidParams,
+                `Elicitation requestedSchema contains unsupported JSON Schema keyword(s) after Standard Schema conversion: ${strippedSchemaPaths.join(', ')}`
+            );
+        }
+        return { params: parsedParams.data, standardSchema };
+    }
+
+    return { params: formParams };
+}