Query 360+ years of US case law via the Harvard Caselaw Access Project
The Caselaw Access Project (CAP) by Harvard Law School provides free access to 6.9 million US court opinions spanning 360+ years. The REST API enables searching, filtering, and downloading full-text case opinions from all federal and state courts. No authentication required for metadata; API key (free registration) required for full text of post-1923 cases.