implementing-mcp-tools

Implementing MCP Tools

Workflow

Task Progress:
- [ ] Step 1: Create tool file in src/mcp/tools/
- [ ] Step 2: Define Zod schema, name, config, and callback
- [ ] Step 3: Export as default ToolModule
- [ ] Step 4: Register in src/mcp/tools/mod.ts
- [ ] Step 5: Run `deno task ci` to verify

Tool File Template

Every tool follows this structure. Create a new file in src/mcp/tools/.

import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import type { CallToolResult } from "@modelcontextprotocol/sdk/types.js";
import { z } from "zod/v3";

import type { ToolConfig, ToolModule } from "$/shared/types.ts";
import {
  createCallToolErrorResponse,
  createCallToolTextResponse,
} from "$/shared/utils.ts";

// 1. Input schema
const schema = z.object({
  myField: z.string().min(1, "Required").describe("What this field does"),
});

// 2. Tool name (kebab-case)
const name = "my-tool-name";

// 3. Config
// deno-lint-ignore no-explicit-any
const config: ToolConfig<typeof schema.shape, any> = {
  title: "Human-readable title",
  description: "What this tool does — shown to the LLM",
  inputSchema: schema.shape,
};

// 4. Callback factory: receives McpServer, returns the handler
// deno-lint-ignore no-explicit-any
const callback = (_mcp: McpServer) => async (args: any): Promise<CallToolResult> => {
  const parsed = schema.safeParse(args);
  if (!parsed.success) {
    return createCallToolErrorResponse({
      error: "Invalid arguments",
      details: parsed.error.flatten(),
      received: args,
    });
  }

  const { myField } = parsed.data;

  // ... tool logic ...

  return createCallToolTextResponse({ result: myField });
};

// 5. Export as ToolModule tuple
// deno-lint-ignore no-explicit-any
const module: ToolModule<typeof schema.shape, any> = [name, config, callback];

export default module;

Registration

In src/mcp/tools/mod.ts:

1. Import the tool: import myTool from "./myTool.ts";
2. Add it to the tools array: