Castle is a cybersecurity software company based in Brooklyn, New York, with a presence in San Francisco. Founded by Johan Brissmyr and Sebastian Wallin, Castle focuses on identity and fraud risk management. The company offers a developer-friendly platform designed to stop bots, prevent account takeovers, and combat various forms of online fraud in real time.

Castle's core product is a risk management platform that uses machine learning to detect and block malicious bots and human attackers automatically. It provides real-time signals based on user behavior, allowing for security decisions without relying on CAPTCHAs. The platform supports both edge and server protection and includes SDKs for easy integration with common programming environments. Key features include bot detection, account takeover prevention, fraud mitigation, risk-based authentication, and real-time policy adjustments. Castle serves security and fraud teams across various industries, including e-commerce and financial services, with a subscription-based model that offers access to a suite of APIs and tools for effective monitoring and response to threats.