What is MCP? — sample code
Two real, runnable MCP servers for the video — one that reads the world and one that writes to it — plus a boilerplate template to build your own. No API keys. Runs on Windows, macOS, and Linux.
▶️ Video: _(link at publish)_ · 📬 Newsletter: _(link)_
What's here
| File | Does | Shows | |---|---|---| | weather_server.py | live weather for any city (Open-Meteo, keyless) | a read tool — your AI reaching the real world | | tasks_server.py | a to-do list it can add to / complete / list | write tools — your AI taking action and changing state | | server_template.py | boilerplate to copy | how to build your own | | client.py | tests both servers without Claude | |
1. Test it in 2 minutes (no Claude needed)
Install uv (one line, any OS), then from this folder: ``bash uv run python client.py ` You'll see a read demo and a write demo: `` weather_server.py tools: ['get_weather'] get_weather({'city': 'Tokyo'}) -> Tokyo, Japan: 21.7°C, mainly clear, wind 4.4 km/h.
tasks_server.py tools: ['add_task', 'complete_task', 'list_tasks'] add_task({'task': 'record episode 2'}) -> Added: 'record episode 2' (you now have 1 task(s)). complete_task({'number': 1}) -> Completed: 'record episode 2'. list_tasks({}) -> 1. [x] record episode 2 `` The tasks server writes to a tasks.json` right next to it — open the file and you'll see exactly what your AI changed.
2. Connect them to Claude
- macOS —
~/Library/Application Support/Claude/claude_desktop_config.json - Windows —
%APPDATA%\Claude\claude_desktop_config.json
{
"mcpServers": {
"weather": { "command": "uv", "args": ["--directory", "ABSOLUTE/PATH/TO/THIS/FOLDER", "run", "python", "weather_server.py"] },
"tasks": { "command": "uv", "args": ["--directory", "ABSOLUTE/PATH/TO/THIS/FOLDER", "run", "python", "tasks_server.py"] }
}
}Restart Claude, then try:
- Read: "What's the weather in Tokyo right now?"
- Write: "Add 'finish the thumbnail' to my tasks." → then "What's on my list?"
3. Build your own
Open server_template.py, rename the server, and replace do_something with your tool — read a file, hit an API, write to a database. Uncomment the resource/prompt examples for those too, then point Claude at it the same way.
Read vs. write — and the one safety note
weather_server only reads. tasks_server writes (it changes tasks.json). That write power — letting your AI actually do things — is the whole point of MCP. It's also exactly why you only connect servers you trust, and why real tools add confirmations and permissions before destructive actions.
Why it's cross-platform
Pure Python + the standard library for HTTP (urllib), local files via pathlib, and sys.executable to launch servers — no OS-specific paths or shells. Only dependency: the mcp SDK.
MIT licensed. Built for the AI Makes Sense channel.
