# Test MCP

> Build and test MCP tools using direct API calls or MCP Inspector. Use when testing tool changes, verifying API responses, debugging MCP tools, or investigating what an API endpoint returns.

- Skill: `tomaspavlin/test-mcp` (Agent Skill)
- Install (CLI): `npx skillmds add tomaspavlin/test-mcp`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomaspavlin/test-mcp/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: tomaspavlin (https://skillmd.com/u/tomaspavlin)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/tomaspavlin/test-mcp

---


# Testing MCP Tools

Use this skill whenever you need to:
- **Investigate** what an API endpoint returns (e.g. before updating a tool's field mappings)
- **Verify** that tool changes correctly map API response fields
- **Debug** why a tool returns wrong or missing data
- **Test** tool changes after implementation

## 1. Build the project

Run `npm run build` to compile TypeScript. Fix any compilation errors before proceeding.

## 2. Call the API directly

Call API methods directly using Node with the `.env` file for credentials:

```bash
node --env-file=.env --input-type=module -e "
import { RohlikAPI } from './dist/rohlik-api.js';
const api = new RohlikAPI({ username: process.env.ROHLIK_USERNAME, password: process.env.ROHLIK_PASSWORD });
const result = await api.methodName(args);
console.log(JSON.stringify(result, null, 2));
"
```

Replace `methodName` and `args` with the appropriate API method. Check `src/rohlik-api.ts` for available methods.

This lets you inspect the raw API response shape to understand what fields are available, verify field names, and confirm your tool's output matches the actual data.

## 3. MCP Inspector (manual testing)

If the user wants to test the full MCP tool flow (not just the API), tell them to run `npm run inspect` in a separate terminal. The Inspector provides a web UI to invoke individual MCP tools with custom arguments.

If the user provides a specific tool name via `$ARGUMENTS`, suggest they test that tool.

## 4. Debugging with console.error

MCP servers communicate over stdout (used for the JSON-RPC protocol), so `console.log` output is invisible in the Inspector.

**Always use `console.error` for debug logging.** It writes to stderr, which is visible in the terminal where the Inspector was launched.

Example:
```typescript
console.error('[ROHLIK_DEBUG] Response:', JSON.stringify(response, null, 2));
```

**Remember to remove debug logging before committing.**

## 5. Unit tests

For logic-only changes (no API calls), run `npm test` to execute unit tests. Use `npm run test:watch` during development.