registerTool
Registers a tool, its schemas, and the view that renders its result.
registerTool declares one tool on the server. It returns the server, therefore you can chain the
calls.
server.registerTool(
{
name: "create_poll",
title: "Create poll",
description: "Create a poll and render it as an interactive view.",
inputSchema: { question: z.string().min(1) },
outputSchema: { pollId: z.string(), total: z.number() },
view: { component: "poll" },
},
(args, extra) => ({
content: `Created poll "${args.question}".`,
structuredContent: { pollId: "1", total: 0 },
}),
);Config
| Field | Type | Purpose |
|---|---|---|
name |
string | The identifier of the tool. The model uses it. |
title |
string, optional | A label for people. |
description |
string, optional | Tells the model when to call the tool. |
inputSchema |
Zod shape, optional | The arguments. The server validates them and infers the type of args. |
outputSchema |
Zod shape, optional | The shape of structuredContent. |
annotations |
ToolAnnotations, optional |
The standard MCP annotations. |
view |
ViewConfig, optional |
The view that renders the result. |
securitySchemes |
SecurityScheme[], optional |
The auth schemes that the tool supports. |
_meta |
ToolMeta, optional |
More metadata for the host. |
view
Set view.component to the name of a registered view. The value is checked against the
ViewNameRegistry interface, which the view generator keeps current.
The other fields of view control the presentation and the CSP of the iframe. See
Content Security Policy.
securitySchemes
securitySchemes: [{ type: "noauth" }, { type: "oauth2", scopes: ["read"] }];The list tells a client which tools need a sign-in. If you list noauth and oauth2 together, the
tool works for an anonymous caller, and it gives more to a caller who signed in.
Handler
(args, extra) => result | Promise<result>args holds the parsed input. Its type comes from inputSchema.
extra is the request context of the SDK. Its _meta field also carries the
client hints of an Apps SDK host.
The handler returns an object with a content field, and an optional structuredContent field and
_meta field. content accepts a plain string, one content block, or an array of content blocks.
The server normalizes each form. See content helpers.
Types accumulate
Each call adds the input, output and _meta shape of that tool to the type of the server.
Therefore typeof server carries enough information for
injectAppHelpers to give you typed, tool-name-narrowed helpers in
the view.
For this to work, export the server type from the same module:
export function createMcpServer() {
return new McpServer(/* … */).registerTool(/* … */);
}
export type AppServer = ReturnType<typeof createMcpServer>;