Allow enum in registerPrompt argsSchema

README.md

@@ -268,6 +268,7 @@ server.registerPrompt(
   {
     title: "Code Review",
     description: "Review code for best practices and potential issues",
+    // can use string or enum
     argsSchema: { code: z.string() }
   },
   ({ code }) => ({

src/server/mcp.test.ts

@@ -4010,6 +4010,69 @@ describe("Tool title precedence", () => {
   });
 });
 
+  test("registerPrompt schema should support strings and enums", async () => {
+    const mcpServer = new McpServer({
+      name: "test server",
+      version: "1.0",
+    });
+
+    const client = new Client({
+      name: "test client",
+      version: "1.0",
+    });
+
+    mcpServer.registerPrompt(
+      "test-prompt",
+      {
+        title: "Team Greeting",
+        description: "Generate a greeting for team members",
+        argsSchema: {
+          name: z.string(),
+          visibility: z.enum(["public", "private"]).optional().default("private"),
+        }
+      },
+      async ({ name, visibility }) => ({
+        messages: [
+          {
+            role: "assistant",
+            content: {
+              type: "text",
+              text: `Creating a new project named ${name} with visibility ${visibility}.`,
+            },
+          },
+        ],
+      }),
+    );
+
+    const [clientTransport, serverTransport] =
+      InMemoryTransport.createLinkedPair();
+
+    await Promise.all([
+      client.connect(clientTransport),
+      mcpServer.server.connect(serverTransport),
+    ]);
+
+    const result1 = await client.getPrompt({
+      name: "test-prompt",
+      arguments: {
+        name: "Test Project",
+        visibility: "public"
+      }
+    });
+
+    expect(result1.messages[0].content.text).toBe("Creating a new project named Test Project with visibility public.");
+
+    await expect(
+      client.getPrompt({
+        name: "test-prompt",
+        arguments: {
+          name: "Test Project",
+          visibility: "foo"
+        }
+      }),
+    ).rejects.toThrow();
+});
+
 describe("elicitInput()", () => {
 
   const checkAvailability = jest.fn().mockResolvedValue(false);

src/server/mcp.ts

@@ -10,6 +10,8 @@ import {
   ZodType,
   ZodTypeDef,
   ZodOptional,
+  ZodDefault,
+  ZodEnum,
 } from "zod";
 import {
   Implementation,
@@ -1246,7 +1248,11 @@ export type RegisteredResourceTemplate = {
 type PromptArgsRawShape = {
   [k: string]:
   | ZodType<string, ZodTypeDef, string>
-  | ZodOptional<ZodType<string, ZodTypeDef, string>>;
+  | ZodEnum<[string, ...string[]]>
+  | ZodDefault<ZodEnum<[string, ...string[]]>>
+  | ZodDefault<ZodOptional<ZodEnum<[string, ...string[]]>>>
+  | ZodOptional<ZodType<string, ZodTypeDef, string>>
+  | ZodDefault<ZodOptional<ZodType<string, ZodTypeDef, string>>>;
 };
 
 export type PromptCallback<

src/types.ts

@@ -685,7 +685,10 @@ export const GetPromptRequestSchema = RequestSchema.extend({
     /**
      * Arguments to use for templating the prompt.
      */
-    arguments: z.optional(z.record(z.string())),
+    arguments: z.optional(z.record(z.union([
+      z.string(),
+      z.object({ type: z.literal("enum"), enum: z.array(z.string()) })
+    ]))),
   }),
 });