Update README.md about client.callTool

[funwarioisii]

Motivation and Context

The Writing MCP Clients in the README did not work correctly and I want to fix it.

How Has This Been Tested?

I used @modelcontextprotocol/server-puppeteer to check the operation at hand

const transport = new StdioClientTransport({
	command: "npx",
	args: ["-y", "@modelcontextprotocol/server-puppeteer"],
});

const client = new Client(
	{
		name: "example-client",
		version: "1.0.0",
	},
	{
		capabilities: {
			prompts: {},
			resources: {},
			tools: {},
		},
	},
);

await client.connect(transport);

const result = await client.callTool({
  name: "puppeteer_navigate",
  arguments: {
		url: "https://google.com",
	},
});
console.dir(result, { depth: null });

await client.close();

Breaking Changes

No.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

The type declaration for client.callTool can be found here.

typescript-sdk/src/client/index.ts

Lines 404 to 406 in 87197fb

	async callTool(
	params: CallToolRequest["params"],
	resultSchema:

typescript-sdk/src/types.ts

Lines 773 to 779 in 87197fb

	export const CallToolRequestSchema = RequestSchema.extend({
	method: z.literal("tools/call"),
	params: BaseRequestParamsSchema.extend({
	name: z.string(),
	arguments: z.optional(z.record(z.unknown())),
	}),
	});

Following the current documentation would result in the following type error

error TS2345: Argument of type 'string' is not assignable to parameter of type '{ [x: string]: unknown; name: string; _meta?: { [x: string]: unknown; progressToken?: string | number | undefined; } | undefined; arguments?: { [x: string]: unknown; } | undefined; }'

I have corrected this diff.

[jspahrsummers]

Thank you!