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callTool

Calls a tool on the MCP server.

Will throw an error if:

  • The server did not declare 'tools' in the capabilities section.
  • The server did not name this tool in the tools list.
  • The tool call fails.

Syntax​

app.callTool(name: string, arguments?: any): Promise<any>

Parameters​

  • name: The name of the tool to call
  • arguments: Optional arguments to pass to the tool

Returns​

A Promise that resolves to the tool's response.

Example​

import { mcpShell } from 'expect-mcp';
import { test, expect } from 'vitest';

test('call a tool on the server', async () => {
  const app = mcpShell('node file-server.js');
  await app.initialize();

  // Call the read_file tool
  const result = await app.callTool('read_file', {
    path: '/path/to/file.txt',
  });

  expect(result).toBeDefined();
  expect(result.content).toBeDefined();

  app.close();
});

Error Handling​

If the tool call fails, the server will return an error response:

const result = await app.callTool('nonexistent_tool', {});

expect(result).toHaveMCPError();

Timeout Configuration​

You can configure the timeout for tool calls using the requestTimeout option:

const app = mcpShell('node slow-server.js', {
  requestTimeout: 30000, // 30 seconds
});

const result = await app.callTool('slow_operation', {});

See Also​