Open & Free Data APIs
Free APIs are good enough for learning and research but carry fragility that keeps them out of production pipelines.
Free data has quietly become good enough to learn and prototype on. yfinance scrapes Yahoo Finance endpoints into tidy DataFrames, Stooq serves long daily histories with no API key, Alpha Vantage offers key-based REST access to prices, fundamentals, and technical indicators, and regulators publish raw exchange files such as EDGAR filings and CME settlement data that cost nothing. These sources are excellent for research, teaching, and cross-checking paid feeds. Their pitfalls are equally real: unofficial scrapers break without warning, rate limits throttle production jobs, adjustment conventions are inconsistent, and delisted symbols quietly vanish. Treat free APIs as a research input, never as the foundation of a trading pipeline.