What Free API Surprised You The Most?

I've been building Python toolkits for free APIs for the past few months. Some of them blew my mind — I had no idea these existed. My top 3 surprises: 1. Crossref — Every DOI Ever Assigned I didn't know there was a free API that holds metadata for 150 million scholarly articles. No API key. No signup. Just send a GET request. import requests article = requests.get("https://api.crossref.org/works/10.1038/nature12373").json()["message"] print(f"{article['title'][0]} — cited {article['is-referenced-by-count']} times") Every DOI you've ever seen? The metadata lives in Crossref. 2. USGS Earthquake API — Every Earthquake in Real Time Every earthquake on Earth, updated every minute. Free. No key. resp = requests.get("https://earthquake.usgs.gov/fdsnws/event/1/query", params={"format": "geojson", "minmagnitude": 5, "limit": 3}).json() for eq in resp['features']: print(f"M{eq['properties']['mag']} — {eq['properties']['place']}") 3. Open-Meteo — Weather Without API Key Most weather APIs charge m