MCP Tool Discovery Guide

MCP Tool Discovery Guide

Overview

This skill helps you discover and correctly use MCP tools exposed through the Code Executor MCP server.

Naming Conventions

MCP tools use different naming conventions at different levels:

All three are valid for imports. Use whichever you prefer.

The .call() Pattern

All tool exports are objects with a .call() method, not direct functions:

// CORRECT
import * as context7 from "../​servers/​context7/​index.js";
await context7.resolveLibraryId.call({ libraryName: "react" });

// INCORRECT - This won't work
await context7.resolveLibraryId({ libraryName: "react" });

Discovering Parameters

Method 1: Check SCHEMA Export

Every tool exports its JSON Schema:

import { resolveLibraryId } from "../​servers/​context7/​index.js";
console.log(resolveLibraryId.SCHEMA);
// Shows: { type: "object", properties: {...}, required: [...] }

Method 2: Use list_server_tools

// Via MCP tool
{ "tool": "list_server_tools", "server": "context7" }

Method 3: Check Generated .d.ts Files

Look in servers/<server>/<tool>.d.ts for TypeScript definitions.

Common Errors and Solutions

"required property missing"

Cause: A required parameter was not provided.

Solution: Check SCHEMA.required array for required parameters.

"invalid enum value"

Cause: Parameter value not in allowed list.

Solution: Check SCHEMA.properties.<param>.enum for valid values.

"Server not connected"

Cause: Server connection not established.

Solution: The wrapper auto-connects, but if you see this error:

1. Check server is configured in mcp.json
2. Check server is enabled (enabled: true)
3. Use check_server_health tool to diagnose

Quick Reference

// Import a server's tools
import * as serverName from "../​servers/<server>/​index.js";

// Check available exports
console.log(Object.keys(serverName));

// Check a tool's schema
console.log(serverName.toolName.SCHEMA);

// Check original tool name
console.log(serverName.toolName.TOOL_NAME);

// Call the tool
const result = await serverName.toolName.call({ param: "value" });

Config Loading (Important for Scripts)

When writing scripts that use custom config paths, you must set environment variables BEFORE importing the mcp module:

// CORRECT - Set env before dynamic import
process.env.CODE_EXECUTOR_MCP_CONFIG = "path/​to/​mcp.json";
const { checkServerHealth } = await import("../​src/​mcp.js");

// WRONG - Import before setting env (ES modules evaluate immediately)
import { checkServerHealth } from "../​src/​mcp.js";
process.env.CODE_EXECUTOR_MCP_CONFIG = "path/​to/​mcp.json"; // Too late!

This is because ES modules are evaluated at import time, and the config is loaded when the module initializes. Setting environment variables after the import has no effect.

Alternative: Use CLI Arguments

If you're running the server directly, use CLI arguments instead:

node build/​server.js --mcp-config /​path/​to/​mcp.json --skills-config /​path/​to/​skills.json

Scripts

This skill includes utility scripts in the scripts/ folder:

discover-tools.ts

Discover all available MCP servers and their tools programmatically:

import { discoverAllServers, discoverServerTools } from './​scripts/​discover-tools.js';

// Discover all servers
const servers = await discoverAllServers();
console.log(servers);

// Discover tools for a specific server
const context7 = await discoverServerTools('context7');
console.log(context7.tools);

Or run directly to print a summary:

import './​scripts/​discover-tools.js';

test-tool-call.ts

Reference script showing the correct pattern for calling MCP tools. Use as a template for testing tool calls.