PolySignal — my Telegram bot that watches Polymarket — has a small subsystem called chain_watcher. It does one thing: cross-check every trade Polymarket's API reports against what actually happened on Polygon, and complain (via Sentry) when the API is wrong.
It's about 280 lines of Python with one dependency — httpx. No web3.py, no eth-account, no eth-abi. I'm going to walk through how to read public on-chain events from Python with nothing but the standard library and an HTTP client, because (a) I needed to and (b) most tutorials reach for the SDK as the first step when you genuinely don't need it for a read-only watcher.
This isn't an anti-SDK argument. If you're signing transactions, sending funds, or doing serious ABI work, use web3.py. The case here is narrower: for reading specific events from a known contract, you can do it cleanly with httpx + JSON-RPC.
What "watching the chain" actually means
A blockchain node exposes a JSON-RPC API. You can ask it questions:
